mm/hugetlb: convert dissolve_free_huge_pages() to folios

[linux-2.6-block.git] / mm / hugetlb.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic hugetlb support.
 * (C) Nadia Yvette Chambers, April 2004
 */
#include <linux/list.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/seq_file.h>
#include <linux/sysctl.h>
#include <linux/highmem.h>
#include <linux/mmu_notifier.h>
#include <linux/nodemask.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/compiler.h>
#include <linux/cpuset.h>
#include <linux/mutex.h>
#include <linux/memblock.h>
#include <linux/sysfs.h>
#include <linux/slab.h>
#include <linux/sched/mm.h>
#include <linux/mmdebug.h>
#include <linux/sched/signal.h>
#include <linux/rmap.h>
#include <linux/string_helpers.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/jhash.h>
#include <linux/numa.h>
#include <linux/llist.h>
#include <linux/cma.h>
#include <linux/migrate.h>
#include <linux/nospec.h>
#include <linux/delayacct.h>
#include <linux/memory.h>
#include <linux/mm_inline.h>
#include <linux/padata.h>

#include <asm/page.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>

#include <linux/io.h>
#include <linux/hugetlb.h>
#include <linux/hugetlb_cgroup.h>
#include <linux/node.h>
#include <linux/page_owner.h>
#include "internal.h"
#include "hugetlb_vmemmap.h"

int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
struct hstate hstates[HUGE_MAX_HSTATE];

#ifdef CONFIG_CMA
static struct cma *hugetlb_cma[MAX_NUMNODES];
static unsigned long hugetlb_cma_size_in_node[MAX_NUMNODES] __initdata;
static bool hugetlb_cma_folio(struct folio *folio, unsigned int order)
{
        return cma_pages_valid(hugetlb_cma[folio_nid(folio)], &folio->page,
                                1 << order);
}
#else
static bool hugetlb_cma_folio(struct folio *folio, unsigned int order)
{
        return false;
}
#endif
static unsigned long hugetlb_cma_size __initdata;

__initdata struct list_head huge_boot_pages[MAX_NUMNODES];

/* for command line parsing */
static struct hstate * __initdata parsed_hstate;
static unsigned long __initdata default_hstate_max_huge_pages;
static bool __initdata parsed_valid_hugepagesz = true;
static bool __initdata parsed_default_hugepagesz;
static unsigned int default_hugepages_in_node[MAX_NUMNODES] __initdata;

/*
 * Protects updates to hugepage_freelists, hugepage_activelist, nr_huge_pages,
 * free_huge_pages, and surplus_huge_pages.
 */
DEFINE_SPINLOCK(hugetlb_lock);

/*
 * Serializes faults on the same logical page.  This is used to
 * prevent spurious OOMs when the hugepage pool is fully utilized.
 */
static int num_fault_mutexes;
struct mutex *hugetlb_fault_mutex_table ____cacheline_aligned_in_smp;

/* Forward declaration */
static int hugetlb_acct_memory(struct hstate *h, long delta);
static void hugetlb_vma_lock_free(struct vm_area_struct *vma);
static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma);
static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
                unsigned long start, unsigned long end);
static struct resv_map *vma_resv_map(struct vm_area_struct *vma);

static inline bool subpool_is_free(struct hugepage_subpool *spool)
{
        if (spool->count)
                return false;
        if (spool->max_hpages != -1)
                return spool->used_hpages == 0;
        if (spool->min_hpages != -1)
                return spool->rsv_hpages == spool->min_hpages;

        return true;
}

static inline void unlock_or_release_subpool(struct hugepage_subpool *spool,
                                                unsigned long irq_flags)
{
        spin_unlock_irqrestore(&spool->lock, irq_flags);

        /* If no pages are used, and no other handles to the subpool
         * remain, give up any reservations based on minimum size and
         * free the subpool */
        if (subpool_is_free(spool)) {
                if (spool->min_hpages != -1)
                        hugetlb_acct_memory(spool->hstate,
                                                -spool->min_hpages);
                kfree(spool);
        }
}

struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
                                                long min_hpages)
{
        struct hugepage_subpool *spool;

        spool = kzalloc(sizeof(*spool), GFP_KERNEL);
        if (!spool)
                return NULL;

        spin_lock_init(&spool->lock);
        spool->count = 1;
        spool->max_hpages = max_hpages;
        spool->hstate = h;
        spool->min_hpages = min_hpages;

        if (min_hpages != -1 && hugetlb_acct_memory(h, min_hpages)) {
                kfree(spool);
                return NULL;
        }
        spool->rsv_hpages = min_hpages;

        return spool;
}

void hugepage_put_subpool(struct hugepage_subpool *spool)
{
        unsigned long flags;

        spin_lock_irqsave(&spool->lock, flags);
        BUG_ON(!spool->count);
        spool->count--;
        unlock_or_release_subpool(spool, flags);
}

/*
 * Subpool accounting for allocating and reserving pages.
 * Return -ENOMEM if there are not enough resources to satisfy the
 * request.  Otherwise, return the number of pages by which the
 * global pools must be adjusted (upward).  The returned value may
 * only be different than the passed value (delta) in the case where
 * a subpool minimum size must be maintained.
 */
static long hugepage_subpool_get_pages(struct hugepage_subpool *spool,
                                      long delta)
{
        long ret = delta;

        if (!spool)
                return ret;

        spin_lock_irq(&spool->lock);

        if (spool->max_hpages != -1) {          /* maximum size accounting */
                if ((spool->used_hpages + delta) <= spool->max_hpages)
                        spool->used_hpages += delta;
                else {
                        ret = -ENOMEM;
                        goto unlock_ret;
                }
        }

        /* minimum size accounting */
        if (spool->min_hpages != -1 && spool->rsv_hpages) {
                if (delta > spool->rsv_hpages) {
                        /*
                         * Asking for more reserves than those already taken on
                         * behalf of subpool.  Return difference.
                         */
                        ret = delta - spool->rsv_hpages;
                        spool->rsv_hpages = 0;
                } else {
                        ret = 0;        /* reserves already accounted for */
                        spool->rsv_hpages -= delta;
                }
        }

unlock_ret:
        spin_unlock_irq(&spool->lock);
        return ret;
}

/*
 * Subpool accounting for freeing and unreserving pages.
 * Return the number of global page reservations that must be dropped.
 * The return value may only be different than the passed value (delta)
 * in the case where a subpool minimum size must be maintained.
 */
static long hugepage_subpool_put_pages(struct hugepage_subpool *spool,
                                       long delta)
{
        long ret = delta;
        unsigned long flags;

        if (!spool)
                return delta;

        spin_lock_irqsave(&spool->lock, flags);

        if (spool->max_hpages != -1)            /* maximum size accounting */
                spool->used_hpages -= delta;

         /* minimum size accounting */
        if (spool->min_hpages != -1 && spool->used_hpages < spool->min_hpages) {
                if (spool->rsv_hpages + delta <= spool->min_hpages)
                        ret = 0;
                else
                        ret = spool->rsv_hpages + delta - spool->min_hpages;

                spool->rsv_hpages += delta;
                if (spool->rsv_hpages > spool->min_hpages)
                        spool->rsv_hpages = spool->min_hpages;
        }

        /*
         * If hugetlbfs_put_super couldn't free spool due to an outstanding
         * quota reference, free it now.
         */
        unlock_or_release_subpool(spool, flags);

        return ret;
}

static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
{
        return HUGETLBFS_SB(inode->i_sb)->spool;
}

static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
{
        return subpool_inode(file_inode(vma->vm_file));
}

/*
 * hugetlb vma_lock helper routines
 */
void hugetlb_vma_lock_read(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                down_read(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                down_read(&resv_map->rw_sema);
        }
}

void hugetlb_vma_unlock_read(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                up_read(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                up_read(&resv_map->rw_sema);
        }
}

void hugetlb_vma_lock_write(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                down_write(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                down_write(&resv_map->rw_sema);
        }
}

void hugetlb_vma_unlock_write(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                up_write(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                up_write(&resv_map->rw_sema);
        }
}

int hugetlb_vma_trylock_write(struct vm_area_struct *vma)
{

        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                return down_write_trylock(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                return down_write_trylock(&resv_map->rw_sema);
        }

        return 1;
}

void hugetlb_vma_assert_locked(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                lockdep_assert_held(&vma_lock->rw_sema);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                lockdep_assert_held(&resv_map->rw_sema);
        }
}

void hugetlb_vma_lock_release(struct kref *kref)
{
        struct hugetlb_vma_lock *vma_lock = container_of(kref,
                        struct hugetlb_vma_lock, refs);

        kfree(vma_lock);
}

static void __hugetlb_vma_unlock_write_put(struct hugetlb_vma_lock *vma_lock)
{
        struct vm_area_struct *vma = vma_lock->vma;

        /*
         * vma_lock structure may or not be released as a result of put,
         * it certainly will no longer be attached to vma so clear pointer.
         * Semaphore synchronizes access to vma_lock->vma field.
         */
        vma_lock->vma = NULL;
        vma->vm_private_data = NULL;
        up_write(&vma_lock->rw_sema);
        kref_put(&vma_lock->refs, hugetlb_vma_lock_release);
}

static void __hugetlb_vma_unlock_write_free(struct vm_area_struct *vma)
{
        if (__vma_shareable_lock(vma)) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                __hugetlb_vma_unlock_write_put(vma_lock);
        } else if (__vma_private_lock(vma)) {
                struct resv_map *resv_map = vma_resv_map(vma);

                /* no free for anon vmas, but still need to unlock */
                up_write(&resv_map->rw_sema);
        }
}

static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
{
        /*
         * Only present in sharable vmas.
         */
        if (!vma || !__vma_shareable_lock(vma))
                return;

        if (vma->vm_private_data) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                down_write(&vma_lock->rw_sema);
                __hugetlb_vma_unlock_write_put(vma_lock);
        }
}

static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma)
{
        struct hugetlb_vma_lock *vma_lock;

        /* Only establish in (flags) sharable vmas */
        if (!vma || !(vma->vm_flags & VM_MAYSHARE))
                return;

        /* Should never get here with non-NULL vm_private_data */
        if (vma->vm_private_data)
                return;

        vma_lock = kmalloc(sizeof(*vma_lock), GFP_KERNEL);
        if (!vma_lock) {
                /*
                 * If we can not allocate structure, then vma can not
                 * participate in pmd sharing.  This is only a possible
                 * performance enhancement and memory saving issue.
                 * However, the lock is also used to synchronize page
                 * faults with truncation.  If the lock is not present,
                 * unlikely races could leave pages in a file past i_size
                 * until the file is removed.  Warn in the unlikely case of
                 * allocation failure.
                 */
                pr_warn_once("HugeTLB: unable to allocate vma specific lock\n");
                return;
        }

        kref_init(&vma_lock->refs);
        init_rwsem(&vma_lock->rw_sema);
        vma_lock->vma = vma;
        vma->vm_private_data = vma_lock;
}

/* Helper that removes a struct file_region from the resv_map cache and returns
 * it for use.
 */
static struct file_region *
get_file_region_entry_from_cache(struct resv_map *resv, long from, long to)
{
        struct file_region *nrg;

        VM_BUG_ON(resv->region_cache_count <= 0);

        resv->region_cache_count--;
        nrg = list_first_entry(&resv->region_cache, struct file_region, link);
        list_del(&nrg->link);

        nrg->from = from;
        nrg->to = to;

        return nrg;
}

static void copy_hugetlb_cgroup_uncharge_info(struct file_region *nrg,
                                              struct file_region *rg)
{
#ifdef CONFIG_CGROUP_HUGETLB
        nrg->reservation_counter = rg->reservation_counter;
        nrg->css = rg->css;
        if (rg->css)
                css_get(rg->css);
#endif
}

/* Helper that records hugetlb_cgroup uncharge info. */
static void record_hugetlb_cgroup_uncharge_info(struct hugetlb_cgroup *h_cg,
                                                struct hstate *h,
                                                struct resv_map *resv,
                                                struct file_region *nrg)
{
#ifdef CONFIG_CGROUP_HUGETLB
        if (h_cg) {
                nrg->reservation_counter =
                        &h_cg->rsvd_hugepage[hstate_index(h)];
                nrg->css = &h_cg->css;
                /*
                 * The caller will hold exactly one h_cg->css reference for the
                 * whole contiguous reservation region. But this area might be
                 * scattered when there are already some file_regions reside in
                 * it. As a result, many file_regions may share only one css
                 * reference. In order to ensure that one file_region must hold
                 * exactly one h_cg->css reference, we should do css_get for
                 * each file_region and leave the reference held by caller
                 * untouched.
                 */
                css_get(&h_cg->css);
                if (!resv->pages_per_hpage)
                        resv->pages_per_hpage = pages_per_huge_page(h);
                /* pages_per_hpage should be the same for all entries in
                 * a resv_map.
                 */
                VM_BUG_ON(resv->pages_per_hpage != pages_per_huge_page(h));
        } else {
                nrg->reservation_counter = NULL;
                nrg->css = NULL;
        }
#endif
}

static void put_uncharge_info(struct file_region *rg)
{
#ifdef CONFIG_CGROUP_HUGETLB
        if (rg->css)
                css_put(rg->css);
#endif
}

static bool has_same_uncharge_info(struct file_region *rg,
                                   struct file_region *org)
{
#ifdef CONFIG_CGROUP_HUGETLB
        return rg->reservation_counter == org->reservation_counter &&
               rg->css == org->css;

#else
        return true;
#endif
}

static void coalesce_file_region(struct resv_map *resv, struct file_region *rg)
{
        struct file_region *nrg, *prg;

        prg = list_prev_entry(rg, link);
        if (&prg->link != &resv->regions && prg->to == rg->from &&
            has_same_uncharge_info(prg, rg)) {
                prg->to = rg->to;

                list_del(&rg->link);
                put_uncharge_info(rg);
                kfree(rg);

                rg = prg;
        }

        nrg = list_next_entry(rg, link);
        if (&nrg->link != &resv->regions && nrg->from == rg->to &&
            has_same_uncharge_info(nrg, rg)) {
                nrg->from = rg->from;

                list_del(&rg->link);
                put_uncharge_info(rg);
                kfree(rg);
        }
}

static inline long
hugetlb_resv_map_add(struct resv_map *map, struct list_head *rg, long from,
                     long to, struct hstate *h, struct hugetlb_cgroup *cg,
                     long *regions_needed)
{
        struct file_region *nrg;

        if (!regions_needed) {
                nrg = get_file_region_entry_from_cache(map, from, to);
                record_hugetlb_cgroup_uncharge_info(cg, h, map, nrg);
                list_add(&nrg->link, rg);
                coalesce_file_region(map, nrg);
        } else
                *regions_needed += 1;

        return to - from;
}

/*
 * Must be called with resv->lock held.
 *
 * Calling this with regions_needed != NULL will count the number of pages
 * to be added but will not modify the linked list. And regions_needed will
 * indicate the number of file_regions needed in the cache to carry out to add
 * the regions for this range.
 */
static long add_reservation_in_range(struct resv_map *resv, long f, long t,
                                     struct hugetlb_cgroup *h_cg,
                                     struct hstate *h, long *regions_needed)
{
        long add = 0;
        struct list_head *head = &resv->regions;
        long last_accounted_offset = f;
        struct file_region *iter, *trg = NULL;
        struct list_head *rg = NULL;

        if (regions_needed)
                *regions_needed = 0;

        /* In this loop, we essentially handle an entry for the range
         * [last_accounted_offset, iter->from), at every iteration, with some
         * bounds checking.
         */
        list_for_each_entry_safe(iter, trg, head, link) {
                /* Skip irrelevant regions that start before our range. */
                if (iter->from < f) {
                        /* If this region ends after the last accounted offset,
                         * then we need to update last_accounted_offset.
                         */
                        if (iter->to > last_accounted_offset)
                                last_accounted_offset = iter->to;
                        continue;
                }

                /* When we find a region that starts beyond our range, we've
                 * finished.
                 */
                if (iter->from >= t) {
                        rg = iter->link.prev;
                        break;
                }

                /* Add an entry for last_accounted_offset -> iter->from, and
                 * update last_accounted_offset.
                 */
                if (iter->from > last_accounted_offset)
                        add += hugetlb_resv_map_add(resv, iter->link.prev,
                                                    last_accounted_offset,
                                                    iter->from, h, h_cg,
                                                    regions_needed);

                last_accounted_offset = iter->to;
        }

        /* Handle the case where our range extends beyond
         * last_accounted_offset.
         */
        if (!rg)
                rg = head->prev;
        if (last_accounted_offset < t)
                add += hugetlb_resv_map_add(resv, rg, last_accounted_offset,
                                            t, h, h_cg, regions_needed);

        return add;
}

/* Must be called with resv->lock acquired. Will drop lock to allocate entries.
 */
static int allocate_file_region_entries(struct resv_map *resv,
                                        int regions_needed)
        __must_hold(&resv->lock)
{
        LIST_HEAD(allocated_regions);
        int to_allocate = 0, i = 0;
        struct file_region *trg = NULL, *rg = NULL;

        VM_BUG_ON(regions_needed < 0);

        /*
         * Check for sufficient descriptors in the cache to accommodate
         * the number of in progress add operations plus regions_needed.
         *
         * This is a while loop because when we drop the lock, some other call
         * to region_add or region_del may have consumed some region_entries,
         * so we keep looping here until we finally have enough entries for
         * (adds_in_progress + regions_needed).
         */
        while (resv->region_cache_count <
               (resv->adds_in_progress + regions_needed)) {
                to_allocate = resv->adds_in_progress + regions_needed -
                              resv->region_cache_count;

                /* At this point, we should have enough entries in the cache
                 * for all the existing adds_in_progress. We should only be
                 * needing to allocate for regions_needed.
                 */
                VM_BUG_ON(resv->region_cache_count < resv->adds_in_progress);

                spin_unlock(&resv->lock);
                for (i = 0; i < to_allocate; i++) {
                        trg = kmalloc(sizeof(*trg), GFP_KERNEL);
                        if (!trg)
                                goto out_of_memory;
                        list_add(&trg->link, &allocated_regions);
                }

                spin_lock(&resv->lock);

                list_splice(&allocated_regions, &resv->region_cache);
                resv->region_cache_count += to_allocate;
        }

        return 0;

out_of_memory:
        list_for_each_entry_safe(rg, trg, &allocated_regions, link) {
                list_del(&rg->link);
                kfree(rg);
        }
        return -ENOMEM;
}

/*
 * Add the huge page range represented by [f, t) to the reserve
 * map.  Regions will be taken from the cache to fill in this range.
 * Sufficient regions should exist in the cache due to the previous
 * call to region_chg with the same range, but in some cases the cache will not
 * have sufficient entries due to races with other code doing region_add or
 * region_del.  The extra needed entries will be allocated.
 *
 * regions_needed is the out value provided by a previous call to region_chg.
 *
 * Return the number of new huge pages added to the map.  This number is greater
 * than or equal to zero.  If file_region entries needed to be allocated for
 * this operation and we were not able to allocate, it returns -ENOMEM.
 * region_add of regions of length 1 never allocate file_regions and cannot
 * fail; region_chg will always allocate at least 1 entry and a region_add for
 * 1 page will only require at most 1 entry.
 */
static long region_add(struct resv_map *resv, long f, long t,
                       long in_regions_needed, struct hstate *h,
                       struct hugetlb_cgroup *h_cg)
{
        long add = 0, actual_regions_needed = 0;

        spin_lock(&resv->lock);
retry:

        /* Count how many regions are actually needed to execute this add. */
        add_reservation_in_range(resv, f, t, NULL, NULL,
                                 &actual_regions_needed);

        /*
         * Check for sufficient descriptors in the cache to accommodate
         * this add operation. Note that actual_regions_needed may be greater
         * than in_regions_needed, as the resv_map may have been modified since
         * the region_chg call. In this case, we need to make sure that we
         * allocate extra entries, such that we have enough for all the
         * existing adds_in_progress, plus the excess needed for this
         * operation.
         */
        if (actual_regions_needed > in_regions_needed &&
            resv->region_cache_count <
                    resv->adds_in_progress +
                            (actual_regions_needed - in_regions_needed)) {
                /* region_add operation of range 1 should never need to
                 * allocate file_region entries.
                 */
                VM_BUG_ON(t - f <= 1);

                if (allocate_file_region_entries(
                            resv, actual_regions_needed - in_regions_needed)) {
                        return -ENOMEM;
                }

                goto retry;
        }

        add = add_reservation_in_range(resv, f, t, h_cg, h, NULL);

        resv->adds_in_progress -= in_regions_needed;

        spin_unlock(&resv->lock);
        return add;
}

/*
 * Examine the existing reserve map and determine how many
 * huge pages in the specified range [f, t) are NOT currently
 * represented.  This routine is called before a subsequent
 * call to region_add that will actually modify the reserve
 * map to add the specified range [f, t).  region_chg does
 * not change the number of huge pages represented by the
 * map.  A number of new file_region structures is added to the cache as a
 * placeholder, for the subsequent region_add call to use. At least 1
 * file_region structure is added.
 *
 * out_regions_needed is the number of regions added to the
 * resv->adds_in_progress.  This value needs to be provided to a follow up call
 * to region_add or region_abort for proper accounting.
 *
 * Returns the number of huge pages that need to be added to the existing
 * reservation map for the range [f, t).  This number is greater or equal to
 * zero.  -ENOMEM is returned if a new file_region structure or cache entry
 * is needed and can not be allocated.
 */
static long region_chg(struct resv_map *resv, long f, long t,
                       long *out_regions_needed)
{
        long chg = 0;

        spin_lock(&resv->lock);

        /* Count how many hugepages in this range are NOT represented. */
        chg = add_reservation_in_range(resv, f, t, NULL, NULL,
                                       out_regions_needed);

        if (*out_regions_needed == 0)
                *out_regions_needed = 1;

        if (allocate_file_region_entries(resv, *out_regions_needed))
                return -ENOMEM;

        resv->adds_in_progress += *out_regions_needed;

        spin_unlock(&resv->lock);
        return chg;
}

/*
 * Abort the in progress add operation.  The adds_in_progress field
 * of the resv_map keeps track of the operations in progress between
 * calls to region_chg and region_add.  Operations are sometimes
 * aborted after the call to region_chg.  In such cases, region_abort
 * is called to decrement the adds_in_progress counter. regions_needed
 * is the value returned by the region_chg call, it is used to decrement
 * the adds_in_progress counter.
 *
 * NOTE: The range arguments [f, t) are not needed or used in this
 * routine.  They are kept to make reading the calling code easier as
 * arguments will match the associated region_chg call.
 */
static void region_abort(struct resv_map *resv, long f, long t,
                         long regions_needed)
{
        spin_lock(&resv->lock);
        VM_BUG_ON(!resv->region_cache_count);
        resv->adds_in_progress -= regions_needed;
        spin_unlock(&resv->lock);
}

/*
 * Delete the specified range [f, t) from the reserve map.  If the
 * t parameter is LONG_MAX, this indicates that ALL regions after f
 * should be deleted.  Locate the regions which intersect [f, t)
 * and either trim, delete or split the existing regions.
 *
 * Returns the number of huge pages deleted from the reserve map.
 * In the normal case, the return value is zero or more.  In the
 * case where a region must be split, a new region descriptor must
 * be allocated.  If the allocation fails, -ENOMEM will be returned.
 * NOTE: If the parameter t == LONG_MAX, then we will never split
 * a region and possibly return -ENOMEM.  Callers specifying
 * t == LONG_MAX do not need to check for -ENOMEM error.
 */
static long region_del(struct resv_map *resv, long f, long t)
{
        struct list_head *head = &resv->regions;
        struct file_region *rg, *trg;
        struct file_region *nrg = NULL;
        long del = 0;

retry:
        spin_lock(&resv->lock);
        list_for_each_entry_safe(rg, trg, head, link) {
                /*
                 * Skip regions before the range to be deleted.  file_region
                 * ranges are normally of the form [from, to).  However, there
                 * may be a "placeholder" entry in the map which is of the form
                 * (from, to) with from == to.  Check for placeholder entries
                 * at the beginning of the range to be deleted.
                 */
                if (rg->to <= f && (rg->to != rg->from || rg->to != f))
                        continue;

                if (rg->from >= t)
                        break;

                if (f > rg->from && t < rg->to) { /* Must split region */
                        /*
                         * Check for an entry in the cache before dropping
                         * lock and attempting allocation.
                         */
                        if (!nrg &&
                            resv->region_cache_count > resv->adds_in_progress) {
                                nrg = list_first_entry(&resv->region_cache,
                                                        struct file_region,
                                                        link);
                                list_del(&nrg->link);
                                resv->region_cache_count--;
                        }

                        if (!nrg) {
                                spin_unlock(&resv->lock);
                                nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
                                if (!nrg)
                                        return -ENOMEM;
                                goto retry;
                        }

                        del += t - f;
                        hugetlb_cgroup_uncharge_file_region(
                                resv, rg, t - f, false);

                        /* New entry for end of split region */
                        nrg->from = t;
                        nrg->to = rg->to;

                        copy_hugetlb_cgroup_uncharge_info(nrg, rg);

                        INIT_LIST_HEAD(&nrg->link);

                        /* Original entry is trimmed */
                        rg->to = f;

                        list_add(&nrg->link, &rg->link);
                        nrg = NULL;
                        break;
                }

                if (f <= rg->from && t >= rg->to) { /* Remove entire region */
                        del += rg->to - rg->from;
                        hugetlb_cgroup_uncharge_file_region(resv, rg,
                                                            rg->to - rg->from, true);
                        list_del(&rg->link);
                        kfree(rg);
                        continue;
                }

                if (f <= rg->from) {    /* Trim beginning of region */
                        hugetlb_cgroup_uncharge_file_region(resv, rg,
                                                            t - rg->from, false);

                        del += t - rg->from;
                        rg->from = t;
                } else {                /* Trim end of region */
                        hugetlb_cgroup_uncharge_file_region(resv, rg,
                                                            rg->to - f, false);

                        del += rg->to - f;
                        rg->to = f;
                }
        }

        spin_unlock(&resv->lock);
        kfree(nrg);
        return del;
}

/*
 * A rare out of memory error was encountered which prevented removal of
 * the reserve map region for a page.  The huge page itself was free'ed
 * and removed from the page cache.  This routine will adjust the subpool
 * usage count, and the global reserve count if needed.  By incrementing
 * these counts, the reserve map entry which could not be deleted will
 * appear as a "reserved" entry instead of simply dangling with incorrect
 * counts.
 */
void hugetlb_fix_reserve_counts(struct inode *inode)
{
        struct hugepage_subpool *spool = subpool_inode(inode);
        long rsv_adjust;
        bool reserved = false;

        rsv_adjust = hugepage_subpool_get_pages(spool, 1);
        if (rsv_adjust > 0) {
                struct hstate *h = hstate_inode(inode);

                if (!hugetlb_acct_memory(h, 1))
                        reserved = true;
        } else if (!rsv_adjust) {
                reserved = true;
        }

        if (!reserved)
                pr_warn("hugetlb: Huge Page Reserved count may go negative.\n");
}

/*
 * Count and return the number of huge pages in the reserve map
 * that intersect with the range [f, t).
 */
static long region_count(struct resv_map *resv, long f, long t)
{
        struct list_head *head = &resv->regions;
        struct file_region *rg;
        long chg = 0;

        spin_lock(&resv->lock);
        /* Locate each segment we overlap with, and count that overlap. */
        list_for_each_entry(rg, head, link) {
                long seg_from;
                long seg_to;

                if (rg->to <= f)
                        continue;
                if (rg->from >= t)
                        break;

                seg_from = max(rg->from, f);
                seg_to = min(rg->to, t);

                chg += seg_to - seg_from;
        }
        spin_unlock(&resv->lock);

        return chg;
}

/*
 * Convert the address within this vma to the page offset within
 * the mapping, huge page units here.
 */
static pgoff_t vma_hugecache_offset(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long address)
{
        return ((address - vma->vm_start) >> huge_page_shift(h)) +
                        (vma->vm_pgoff >> huge_page_order(h));
}

/**
 * vma_kernel_pagesize - Page size granularity for this VMA.
 * @vma: The user mapping.
 *
 * Folios in this VMA will be aligned to, and at least the size of the
 * number of bytes returned by this function.
 *
 * Return: The default size of the folios allocated when backing a VMA.
 */
unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
{
        if (vma->vm_ops && vma->vm_ops->pagesize)
                return vma->vm_ops->pagesize(vma);
        return PAGE_SIZE;
}
EXPORT_SYMBOL_GPL(vma_kernel_pagesize);

/*
 * Return the page size being used by the MMU to back a VMA. In the majority
 * of cases, the page size used by the kernel matches the MMU size. On
 * architectures where it differs, an architecture-specific 'strong'
 * version of this symbol is required.
 */
__weak unsigned long vma_mmu_pagesize(struct vm_area_struct *vma)
{
        return vma_kernel_pagesize(vma);
}

/*
 * Flags for MAP_PRIVATE reservations.  These are stored in the bottom
 * bits of the reservation map pointer, which are always clear due to
 * alignment.
 */
#define HPAGE_RESV_OWNER    (1UL << 0)
#define HPAGE_RESV_UNMAPPED (1UL << 1)
#define HPAGE_RESV_MASK (HPAGE_RESV_OWNER | HPAGE_RESV_UNMAPPED)

/*
 * These helpers are used to track how many pages are reserved for
 * faults in a MAP_PRIVATE mapping. Only the process that called mmap()
 * is guaranteed to have their future faults succeed.
 *
 * With the exception of hugetlb_dup_vma_private() which is called at fork(),
 * the reserve counters are updated with the hugetlb_lock held. It is safe
 * to reset the VMA at fork() time as it is not in use yet and there is no
 * chance of the global counters getting corrupted as a result of the values.
 *
 * The private mapping reservation is represented in a subtly different
 * manner to a shared mapping.  A shared mapping has a region map associated
 * with the underlying file, this region map represents the backing file
 * pages which have ever had a reservation assigned which this persists even
 * after the page is instantiated.  A private mapping has a region map
 * associated with the original mmap which is attached to all VMAs which
 * reference it, this region map represents those offsets which have consumed
 * reservation ie. where pages have been instantiated.
 */
static unsigned long get_vma_private_data(struct vm_area_struct *vma)
{
        return (unsigned long)vma->vm_private_data;
}

static void set_vma_private_data(struct vm_area_struct *vma,
                                                        unsigned long value)
{
        vma->vm_private_data = (void *)value;
}

static void
resv_map_set_hugetlb_cgroup_uncharge_info(struct resv_map *resv_map,
                                          struct hugetlb_cgroup *h_cg,
                                          struct hstate *h)
{
#ifdef CONFIG_CGROUP_HUGETLB
        if (!h_cg || !h) {
                resv_map->reservation_counter = NULL;
                resv_map->pages_per_hpage = 0;
                resv_map->css = NULL;
        } else {
                resv_map->reservation_counter =
                        &h_cg->rsvd_hugepage[hstate_index(h)];
                resv_map->pages_per_hpage = pages_per_huge_page(h);
                resv_map->css = &h_cg->css;
        }
#endif
}

struct resv_map *resv_map_alloc(void)
{
        struct resv_map *resv_map = kmalloc(sizeof(*resv_map), GFP_KERNEL);
        struct file_region *rg = kmalloc(sizeof(*rg), GFP_KERNEL);

        if (!resv_map || !rg) {
                kfree(resv_map);
                kfree(rg);
                return NULL;
        }

        kref_init(&resv_map->refs);
        spin_lock_init(&resv_map->lock);
        INIT_LIST_HEAD(&resv_map->regions);
        init_rwsem(&resv_map->rw_sema);

        resv_map->adds_in_progress = 0;
        /*
         * Initialize these to 0. On shared mappings, 0's here indicate these
         * fields don't do cgroup accounting. On private mappings, these will be
         * re-initialized to the proper values, to indicate that hugetlb cgroup
         * reservations are to be un-charged from here.
         */
        resv_map_set_hugetlb_cgroup_uncharge_info(resv_map, NULL, NULL);

        INIT_LIST_HEAD(&resv_map->region_cache);
        list_add(&rg->link, &resv_map->region_cache);
        resv_map->region_cache_count = 1;

        return resv_map;
}

void resv_map_release(struct kref *ref)
{
        struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
        struct list_head *head = &resv_map->region_cache;
        struct file_region *rg, *trg;

        /* Clear out any active regions before we release the map. */
        region_del(resv_map, 0, LONG_MAX);

        /* ... and any entries left in the cache */
        list_for_each_entry_safe(rg, trg, head, link) {
                list_del(&rg->link);
                kfree(rg);
        }

        VM_BUG_ON(resv_map->adds_in_progress);

        kfree(resv_map);
}

static inline struct resv_map *inode_resv_map(struct inode *inode)
{
        /*
         * At inode evict time, i_mapping may not point to the original
         * address space within the inode.  This original address space
         * contains the pointer to the resv_map.  So, always use the
         * address space embedded within the inode.
         * The VERY common case is inode->mapping == &inode->i_data but,
         * this may not be true for device special inodes.
         */
        return (struct resv_map *)(&inode->i_data)->i_private_data;
}

static struct resv_map *vma_resv_map(struct vm_area_struct *vma)
{
        VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
        if (vma->vm_flags & VM_MAYSHARE) {
                struct address_space *mapping = vma->vm_file->f_mapping;
                struct inode *inode = mapping->host;

                return inode_resv_map(inode);

        } else {
                return (struct resv_map *)(get_vma_private_data(vma) &
                                                        ~HPAGE_RESV_MASK);
        }
}

static void set_vma_resv_map(struct vm_area_struct *vma, struct resv_map *map)
{
        VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
        VM_BUG_ON_VMA(vma->vm_flags & VM_MAYSHARE, vma);

        set_vma_private_data(vma, (unsigned long)map);
}

static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags)
{
        VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
        VM_BUG_ON_VMA(vma->vm_flags & VM_MAYSHARE, vma);

        set_vma_private_data(vma, get_vma_private_data(vma) | flags);
}

static int is_vma_resv_set(struct vm_area_struct *vma, unsigned long flag)
{
        VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);

        return (get_vma_private_data(vma) & flag) != 0;
}

bool __vma_private_lock(struct vm_area_struct *vma)
{
        return !(vma->vm_flags & VM_MAYSHARE) &&
                get_vma_private_data(vma) & ~HPAGE_RESV_MASK &&
                is_vma_resv_set(vma, HPAGE_RESV_OWNER);
}

void hugetlb_dup_vma_private(struct vm_area_struct *vma)
{
        VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma);
        /*
         * Clear vm_private_data
         * - For shared mappings this is a per-vma semaphore that may be
         *   allocated in a subsequent call to hugetlb_vm_op_open.
         *   Before clearing, make sure pointer is not associated with vma
         *   as this will leak the structure.  This is the case when called
         *   via clear_vma_resv_huge_pages() and hugetlb_vm_op_open has already
         *   been called to allocate a new structure.
         * - For MAP_PRIVATE mappings, this is the reserve map which does
         *   not apply to children.  Faults generated by the children are
         *   not guaranteed to succeed, even if read-only.
         */
        if (vma->vm_flags & VM_MAYSHARE) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                if (vma_lock && vma_lock->vma != vma)
                        vma->vm_private_data = NULL;
        } else
                vma->vm_private_data = NULL;
}

/*
 * Reset and decrement one ref on hugepage private reservation.
 * Called with mm->mmap_lock writer semaphore held.
 * This function should be only used by move_vma() and operate on
 * same sized vma. It should never come here with last ref on the
 * reservation.
 */
void clear_vma_resv_huge_pages(struct vm_area_struct *vma)
{
        /*
         * Clear the old hugetlb private page reservation.
         * It has already been transferred to new_vma.
         *
         * During a mremap() operation of a hugetlb vma we call move_vma()
         * which copies vma into new_vma and unmaps vma. After the copy
         * operation both new_vma and vma share a reference to the resv_map
         * struct, and at that point vma is about to be unmapped. We don't
         * want to return the reservation to the pool at unmap of vma because
         * the reservation still lives on in new_vma, so simply decrement the
         * ref here and remove the resv_map reference from this vma.
         */
        struct resv_map *reservations = vma_resv_map(vma);

        if (reservations && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                resv_map_put_hugetlb_cgroup_uncharge_info(reservations);
                kref_put(&reservations->refs, resv_map_release);
        }

        hugetlb_dup_vma_private(vma);
}

/* Returns true if the VMA has associated reserve pages */
static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
{
        if (vma->vm_flags & VM_NORESERVE) {
                /*
                 * This address is already reserved by other process(chg == 0),
                 * so, we should decrement reserved count. Without decrementing,
                 * reserve count remains after releasing inode, because this
                 * allocated page will go into page cache and is regarded as
                 * coming from reserved pool in releasing step.  Currently, we
                 * don't have any other solution to deal with this situation
                 * properly, so add work-around here.
                 */
                if (vma->vm_flags & VM_MAYSHARE && chg == 0)
                        return true;
                else
                        return false;
        }

        /* Shared mappings always use reserves */
        if (vma->vm_flags & VM_MAYSHARE) {
                /*
                 * We know VM_NORESERVE is not set.  Therefore, there SHOULD
                 * be a region map for all pages.  The only situation where
                 * there is no region map is if a hole was punched via
                 * fallocate.  In this case, there really are no reserves to
                 * use.  This situation is indicated if chg != 0.
                 */
                if (chg)
                        return false;
                else
                        return true;
        }

        /*
         * Only the process that called mmap() has reserves for
         * private mappings.
         */
        if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                /*
                 * Like the shared case above, a hole punch or truncate
                 * could have been performed on the private mapping.
                 * Examine the value of chg to determine if reserves
                 * actually exist or were previously consumed.
                 * Very Subtle - The value of chg comes from a previous
                 * call to vma_needs_reserves().  The reserve map for
                 * private mappings has different (opposite) semantics
                 * than that of shared mappings.  vma_needs_reserves()
                 * has already taken this difference in semantics into
                 * account.  Therefore, the meaning of chg is the same
                 * as in the shared case above.  Code could easily be
                 * combined, but keeping it separate draws attention to
                 * subtle differences.
                 */
                if (chg)
                        return false;
                else
                        return true;
        }

        return false;
}

static void enqueue_hugetlb_folio(struct hstate *h, struct folio *folio)
{
        int nid = folio_nid(folio);

        lockdep_assert_held(&hugetlb_lock);
        VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);

        list_move(&folio->lru, &h->hugepage_freelists[nid]);
        h->free_huge_pages++;
        h->free_huge_pages_node[nid]++;
        folio_set_hugetlb_freed(folio);
}

static struct folio *dequeue_hugetlb_folio_node_exact(struct hstate *h,
                                                                int nid)
{
        struct folio *folio;
        bool pin = !!(current->flags & PF_MEMALLOC_PIN);

        lockdep_assert_held(&hugetlb_lock);
        list_for_each_entry(folio, &h->hugepage_freelists[nid], lru) {
                if (pin && !folio_is_longterm_pinnable(folio))
                        continue;

                if (folio_test_hwpoison(folio))
                        continue;

                list_move(&folio->lru, &h->hugepage_activelist);
                folio_ref_unfreeze(folio, 1);
                folio_clear_hugetlb_freed(folio);
                h->free_huge_pages--;
                h->free_huge_pages_node[nid]--;
                return folio;
        }

        return NULL;
}

static struct folio *dequeue_hugetlb_folio_nodemask(struct hstate *h, gfp_t gfp_mask,
                                                        int nid, nodemask_t *nmask)
{
        unsigned int cpuset_mems_cookie;
        struct zonelist *zonelist;
        struct zone *zone;
        struct zoneref *z;
        int node = NUMA_NO_NODE;

        zonelist = node_zonelist(nid, gfp_mask);

retry_cpuset:
        cpuset_mems_cookie = read_mems_allowed_begin();
        for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nmask) {
                struct folio *folio;

                if (!cpuset_zone_allowed(zone, gfp_mask))
                        continue;
                /*
                 * no need to ask again on the same node. Pool is node rather than
                 * zone aware
                 */
                if (zone_to_nid(zone) == node)
                        continue;
                node = zone_to_nid(zone);

                folio = dequeue_hugetlb_folio_node_exact(h, node);
                if (folio)
                        return folio;
        }
        if (unlikely(read_mems_allowed_retry(cpuset_mems_cookie)))
                goto retry_cpuset;

        return NULL;
}

static unsigned long available_huge_pages(struct hstate *h)
{
        return h->free_huge_pages - h->resv_huge_pages;
}

static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
                                struct vm_area_struct *vma,
                                unsigned long address, int avoid_reserve,
                                long chg)
{
        struct folio *folio = NULL;
        struct mempolicy *mpol;
        gfp_t gfp_mask;
        nodemask_t *nodemask;
        int nid;

        /*
         * A child process with MAP_PRIVATE mappings created by their parent
         * have no page reserves. This check ensures that reservations are
         * not "stolen". The child may still get SIGKILLed
         */
        if (!vma_has_reserves(vma, chg) && !available_huge_pages(h))
                goto err;

        /* If reserves cannot be used, ensure enough pages are in the pool */
        if (avoid_reserve && !available_huge_pages(h))
                goto err;

        gfp_mask = htlb_alloc_mask(h);
        nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);

        if (mpol_is_preferred_many(mpol)) {
                folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask,
                                                        nid, nodemask);

                /* Fallback to all nodes if page==NULL */
                nodemask = NULL;
        }

        if (!folio)
                folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask,
                                                        nid, nodemask);

        if (folio && !avoid_reserve && vma_has_reserves(vma, chg)) {
                folio_set_hugetlb_restore_reserve(folio);
                h->resv_huge_pages--;
        }

        mpol_cond_put(mpol);
        return folio;

err:
        return NULL;
}

/*
 * common helper functions for hstate_next_node_to_{alloc|free}.
 * We may have allocated or freed a huge page based on a different
 * nodes_allowed previously, so h->next_node_to_{alloc|free} might
 * be outside of *nodes_allowed.  Ensure that we use an allowed
 * node for alloc or free.
 */
static int next_node_allowed(int nid, nodemask_t *nodes_allowed)
{
        nid = next_node_in(nid, *nodes_allowed);
        VM_BUG_ON(nid >= MAX_NUMNODES);

        return nid;
}

static int get_valid_node_allowed(int nid, nodemask_t *nodes_allowed)
{
        if (!node_isset(nid, *nodes_allowed))
                nid = next_node_allowed(nid, nodes_allowed);
        return nid;
}

/*
 * returns the previously saved node ["this node"] from which to
 * allocate a persistent huge page for the pool and advance the
 * next node from which to allocate, handling wrap at end of node
 * mask.
 */
static int hstate_next_node_to_alloc(int *next_node,
                                        nodemask_t *nodes_allowed)
{
        int nid;

        VM_BUG_ON(!nodes_allowed);

        nid = get_valid_node_allowed(*next_node, nodes_allowed);
        *next_node = next_node_allowed(nid, nodes_allowed);

        return nid;
}

/*
 * helper for remove_pool_hugetlb_folio() - return the previously saved
 * node ["this node"] from which to free a huge page.  Advance the
 * next node id whether or not we find a free huge page to free so
 * that the next attempt to free addresses the next node.
 */
static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
{
        int nid;

        VM_BUG_ON(!nodes_allowed);

        nid = get_valid_node_allowed(h->next_nid_to_free, nodes_allowed);
        h->next_nid_to_free = next_node_allowed(nid, nodes_allowed);

        return nid;
}

#define for_each_node_mask_to_alloc(next_node, nr_nodes, node, mask)            \
        for (nr_nodes = nodes_weight(*mask);                            \
                nr_nodes > 0 &&                                         \
                ((node = hstate_next_node_to_alloc(next_node, mask)) || 1);     \
                nr_nodes--)

#define for_each_node_mask_to_free(hs, nr_nodes, node, mask)            \
        for (nr_nodes = nodes_weight(*mask);                            \
                nr_nodes > 0 &&                                         \
                ((node = hstate_next_node_to_free(hs, mask)) || 1);     \
                nr_nodes--)

/* used to demote non-gigantic_huge pages as well */
static void __destroy_compound_gigantic_folio(struct folio *folio,
                                        unsigned int order, bool demote)
{
        int i;
        int nr_pages = 1 << order;
        struct page *p;

        atomic_set(&folio->_entire_mapcount, 0);
        atomic_set(&folio->_large_mapcount, 0);
        atomic_set(&folio->_pincount, 0);

        for (i = 1; i < nr_pages; i++) {
                p = folio_page(folio, i);
                p->flags &= ~PAGE_FLAGS_CHECK_AT_FREE;
                p->mapping = NULL;
                clear_compound_head(p);
                if (!demote)
                        set_page_refcounted(p);
        }

        __folio_clear_head(folio);
}

static void destroy_compound_hugetlb_folio_for_demote(struct folio *folio,
                                        unsigned int order)
{
        __destroy_compound_gigantic_folio(folio, order, true);
}

#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
static void destroy_compound_gigantic_folio(struct folio *folio,
                                        unsigned int order)
{
        __destroy_compound_gigantic_folio(folio, order, false);
}

static void free_gigantic_folio(struct folio *folio, unsigned int order)
{
        /*
         * If the page isn't allocated using the cma allocator,
         * cma_release() returns false.
         */
#ifdef CONFIG_CMA
        int nid = folio_nid(folio);

        if (cma_release(hugetlb_cma[nid], &folio->page, 1 << order))
                return;
#endif

        free_contig_range(folio_pfn(folio), 1 << order);
}

#ifdef CONFIG_CONTIG_ALLOC
static struct folio *alloc_gigantic_folio(struct hstate *h, gfp_t gfp_mask,
                int nid, nodemask_t *nodemask)
{
        struct page *page;
        unsigned long nr_pages = pages_per_huge_page(h);
        if (nid == NUMA_NO_NODE)
                nid = numa_mem_id();

#ifdef CONFIG_CMA
        {
                int node;

                if (hugetlb_cma[nid]) {
                        page = cma_alloc(hugetlb_cma[nid], nr_pages,
                                        huge_page_order(h), true);
                        if (page)
                                return page_folio(page);
                }

                if (!(gfp_mask & __GFP_THISNODE)) {
                        for_each_node_mask(node, *nodemask) {
                                if (node == nid || !hugetlb_cma[node])
                                        continue;

                                page = cma_alloc(hugetlb_cma[node], nr_pages,
                                                huge_page_order(h), true);
                                if (page)
                                        return page_folio(page);
                        }
                }
        }
#endif

        page = alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
        return page ? page_folio(page) : NULL;
}

#else /* !CONFIG_CONTIG_ALLOC */
static struct folio *alloc_gigantic_folio(struct hstate *h, gfp_t gfp_mask,
                                        int nid, nodemask_t *nodemask)
{
        return NULL;
}
#endif /* CONFIG_CONTIG_ALLOC */

#else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE */
static struct folio *alloc_gigantic_folio(struct hstate *h, gfp_t gfp_mask,
                                        int nid, nodemask_t *nodemask)
{
        return NULL;
}
static inline void free_gigantic_folio(struct folio *folio,
                                                unsigned int order) { }
static inline void destroy_compound_gigantic_folio(struct folio *folio,
                                                unsigned int order) { }
#endif

/*
 * Remove hugetlb folio from lists.
 * If vmemmap exists for the folio, clear the hugetlb flag so that the
 * folio appears as just a compound page.  Otherwise, wait until after
 * allocating vmemmap to clear the flag.
 *
 * A reference is held on the folio, except in the case of demote.
 *
 * Must be called with hugetlb lock held.
 */
static void __remove_hugetlb_folio(struct hstate *h, struct folio *folio,
                                                        bool adjust_surplus,
                                                        bool demote)
{
        int nid = folio_nid(folio);

        VM_BUG_ON_FOLIO(hugetlb_cgroup_from_folio(folio), folio);
        VM_BUG_ON_FOLIO(hugetlb_cgroup_from_folio_rsvd(folio), folio);

        lockdep_assert_held(&hugetlb_lock);
        if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                return;

        list_del(&folio->lru);

        if (folio_test_hugetlb_freed(folio)) {
                h->free_huge_pages--;
                h->free_huge_pages_node[nid]--;
        }
        if (adjust_surplus) {
                h->surplus_huge_pages--;
                h->surplus_huge_pages_node[nid]--;
        }

        /*
         * We can only clear the hugetlb flag after allocating vmemmap
         * pages.  Otherwise, someone (memory error handling) may try to write
         * to tail struct pages.
         */
        if (!folio_test_hugetlb_vmemmap_optimized(folio))
                __folio_clear_hugetlb(folio);

         /*
          * In the case of demote we do not ref count the page as it will soon
          * be turned into a page of smaller size.
         */
        if (!demote)
                folio_ref_unfreeze(folio, 1);

        h->nr_huge_pages--;
        h->nr_huge_pages_node[nid]--;
}

static void remove_hugetlb_folio(struct hstate *h, struct folio *folio,
                                                        bool adjust_surplus)
{
        __remove_hugetlb_folio(h, folio, adjust_surplus, false);
}

static void remove_hugetlb_folio_for_demote(struct hstate *h, struct folio *folio,
                                                        bool adjust_surplus)
{
        __remove_hugetlb_folio(h, folio, adjust_surplus, true);
}

static void add_hugetlb_folio(struct hstate *h, struct folio *folio,
                             bool adjust_surplus)
{
        int zeroed;
        int nid = folio_nid(folio);

        VM_BUG_ON_FOLIO(!folio_test_hugetlb_vmemmap_optimized(folio), folio);

        lockdep_assert_held(&hugetlb_lock);

        INIT_LIST_HEAD(&folio->lru);
        h->nr_huge_pages++;
        h->nr_huge_pages_node[nid]++;

        if (adjust_surplus) {
                h->surplus_huge_pages++;
                h->surplus_huge_pages_node[nid]++;
        }

        __folio_set_hugetlb(folio);
        folio_change_private(folio, NULL);
        /*
         * We have to set hugetlb_vmemmap_optimized again as above
         * folio_change_private(folio, NULL) cleared it.
         */
        folio_set_hugetlb_vmemmap_optimized(folio);

        /*
         * This folio is about to be managed by the hugetlb allocator and
         * should have no users.  Drop our reference, and check for others
         * just in case.
         */
        zeroed = folio_put_testzero(folio);
        if (unlikely(!zeroed))
                /*
                 * It is VERY unlikely soneone else has taken a ref
                 * on the folio.  In this case, we simply return as
                 * free_huge_folio() will be called when this other ref
                 * is dropped.
                 */
                return;

        arch_clear_hugetlb_flags(folio);
        enqueue_hugetlb_folio(h, folio);
}

static void __update_and_free_hugetlb_folio(struct hstate *h,
                                                struct folio *folio)
{
        bool clear_flag = folio_test_hugetlb_vmemmap_optimized(folio);

        if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                return;

        /*
         * If we don't know which subpages are hwpoisoned, we can't free
         * the hugepage, so it's leaked intentionally.
         */
        if (folio_test_hugetlb_raw_hwp_unreliable(folio))
                return;

        /*
         * If folio is not vmemmap optimized (!clear_flag), then the folio
         * is no longer identified as a hugetlb page.  hugetlb_vmemmap_restore_folio
         * can only be passed hugetlb pages and will BUG otherwise.
         */
        if (clear_flag && hugetlb_vmemmap_restore_folio(h, folio)) {
                spin_lock_irq(&hugetlb_lock);
                /*
                 * If we cannot allocate vmemmap pages, just refuse to free the
                 * page and put the page back on the hugetlb free list and treat
                 * as a surplus page.
                 */
                add_hugetlb_folio(h, folio, true);
                spin_unlock_irq(&hugetlb_lock);
                return;
        }

        /*
         * Move PageHWPoison flag from head page to the raw error pages,
         * which makes any healthy subpages reusable.
         */
        if (unlikely(folio_test_hwpoison(folio)))
                folio_clear_hugetlb_hwpoison(folio);

        /*
         * If vmemmap pages were allocated above, then we need to clear the
         * hugetlb flag under the hugetlb lock.
         */
        if (folio_test_hugetlb(folio)) {
                spin_lock_irq(&hugetlb_lock);
                __folio_clear_hugetlb(folio);
                spin_unlock_irq(&hugetlb_lock);
        }

        /*
         * Non-gigantic pages demoted from CMA allocated gigantic pages
         * need to be given back to CMA in free_gigantic_folio.
         */
        if (hstate_is_gigantic(h) ||
            hugetlb_cma_folio(folio, huge_page_order(h))) {
                destroy_compound_gigantic_folio(folio, huge_page_order(h));
                free_gigantic_folio(folio, huge_page_order(h));
        } else {
                INIT_LIST_HEAD(&folio->_deferred_list);
                folio_put(folio);
        }
}

/*
 * As update_and_free_hugetlb_folio() can be called under any context, so we cannot
 * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
 * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
 * the vmemmap pages.
 *
 * free_hpage_workfn() locklessly retrieves the linked list of pages to be
 * freed and frees them one-by-one. As the page->mapping pointer is going
 * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
 * structure of a lockless linked list of huge pages to be freed.
 */
static LLIST_HEAD(hpage_freelist);

static void free_hpage_workfn(struct work_struct *work)
{
        struct llist_node *node;

        node = llist_del_all(&hpage_freelist);

        while (node) {
                struct folio *folio;
                struct hstate *h;

                folio = container_of((struct address_space **)node,
                                     struct folio, mapping);
                node = node->next;
                folio->mapping = NULL;
                /*
                 * The VM_BUG_ON_FOLIO(!folio_test_hugetlb(folio), folio) in
                 * folio_hstate() is going to trigger because a previous call to
                 * remove_hugetlb_folio() will clear the hugetlb bit, so do
                 * not use folio_hstate() directly.
                 */
                h = size_to_hstate(folio_size(folio));

                __update_and_free_hugetlb_folio(h, folio);

                cond_resched();
        }
}
static DECLARE_WORK(free_hpage_work, free_hpage_workfn);

static inline void flush_free_hpage_work(struct hstate *h)
{
        if (hugetlb_vmemmap_optimizable(h))
                flush_work(&free_hpage_work);
}

static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
                                 bool atomic)
{
        if (!folio_test_hugetlb_vmemmap_optimized(folio) || !atomic) {
                __update_and_free_hugetlb_folio(h, folio);
                return;
        }

        /*
         * Defer freeing to avoid using GFP_ATOMIC to allocate vmemmap pages.
         *
         * Only call schedule_work() if hpage_freelist is previously
         * empty. Otherwise, schedule_work() had been called but the workfn
         * hasn't retrieved the list yet.
         */
        if (llist_add((struct llist_node *)&folio->mapping, &hpage_freelist))
                schedule_work(&free_hpage_work);
}

static void bulk_vmemmap_restore_error(struct hstate *h,
                                        struct list_head *folio_list,
                                        struct list_head *non_hvo_folios)
{
        struct folio *folio, *t_folio;

        if (!list_empty(non_hvo_folios)) {
                /*
                 * Free any restored hugetlb pages so that restore of the
                 * entire list can be retried.
                 * The idea is that in the common case of ENOMEM errors freeing
                 * hugetlb pages with vmemmap we will free up memory so that we
                 * can allocate vmemmap for more hugetlb pages.
                 */
                list_for_each_entry_safe(folio, t_folio, non_hvo_folios, lru) {
                        list_del(&folio->lru);
                        spin_lock_irq(&hugetlb_lock);
                        __folio_clear_hugetlb(folio);
                        spin_unlock_irq(&hugetlb_lock);
                        update_and_free_hugetlb_folio(h, folio, false);
                        cond_resched();
                }
        } else {
                /*
                 * In the case where there are no folios which can be
                 * immediately freed, we loop through the list trying to restore
                 * vmemmap individually in the hope that someone elsewhere may
                 * have done something to cause success (such as freeing some
                 * memory).  If unable to restore a hugetlb page, the hugetlb
                 * page is made a surplus page and removed from the list.
                 * If are able to restore vmemmap and free one hugetlb page, we
                 * quit processing the list to retry the bulk operation.
                 */
                list_for_each_entry_safe(folio, t_folio, folio_list, lru)
                        if (hugetlb_vmemmap_restore_folio(h, folio)) {
                                list_del(&folio->lru);
                                spin_lock_irq(&hugetlb_lock);
                                add_hugetlb_folio(h, folio, true);
                                spin_unlock_irq(&hugetlb_lock);
                        } else {
                                list_del(&folio->lru);
                                spin_lock_irq(&hugetlb_lock);
                                __folio_clear_hugetlb(folio);
                                spin_unlock_irq(&hugetlb_lock);
                                update_and_free_hugetlb_folio(h, folio, false);
                                cond_resched();
                                break;
                        }
        }
}

static void update_and_free_pages_bulk(struct hstate *h,
                                                struct list_head *folio_list)
{
        long ret;
        struct folio *folio, *t_folio;
        LIST_HEAD(non_hvo_folios);

        /*
         * First allocate required vmemmmap (if necessary) for all folios.
         * Carefully handle errors and free up any available hugetlb pages
         * in an effort to make forward progress.
         */
retry:
        ret = hugetlb_vmemmap_restore_folios(h, folio_list, &non_hvo_folios);
        if (ret < 0) {
                bulk_vmemmap_restore_error(h, folio_list, &non_hvo_folios);
                goto retry;
        }

        /*
         * At this point, list should be empty, ret should be >= 0 and there
         * should only be pages on the non_hvo_folios list.
         * Do note that the non_hvo_folios list could be empty.
         * Without HVO enabled, ret will be 0 and there is no need to call
         * __folio_clear_hugetlb as this was done previously.
         */
        VM_WARN_ON(!list_empty(folio_list));
        VM_WARN_ON(ret < 0);
        if (!list_empty(&non_hvo_folios) && ret) {
                spin_lock_irq(&hugetlb_lock);
                list_for_each_entry(folio, &non_hvo_folios, lru)
                        __folio_clear_hugetlb(folio);
                spin_unlock_irq(&hugetlb_lock);
        }

        list_for_each_entry_safe(folio, t_folio, &non_hvo_folios, lru) {
                update_and_free_hugetlb_folio(h, folio, false);
                cond_resched();
        }
}

struct hstate *size_to_hstate(unsigned long size)
{
        struct hstate *h;

        for_each_hstate(h) {
                if (huge_page_size(h) == size)
                        return h;
        }
        return NULL;
}

void free_huge_folio(struct folio *folio)
{
        /*
         * Can't pass hstate in here because it is called from the
         * generic mm code.
         */
        struct hstate *h = folio_hstate(folio);
        int nid = folio_nid(folio);
        struct hugepage_subpool *spool = hugetlb_folio_subpool(folio);
        bool restore_reserve;
        unsigned long flags;

        VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
        VM_BUG_ON_FOLIO(folio_mapcount(folio), folio);

        hugetlb_set_folio_subpool(folio, NULL);
        if (folio_test_anon(folio))
                __ClearPageAnonExclusive(&folio->page);
        folio->mapping = NULL;
        restore_reserve = folio_test_hugetlb_restore_reserve(folio);
        folio_clear_hugetlb_restore_reserve(folio);

        /*
         * If HPageRestoreReserve was set on page, page allocation consumed a
         * reservation.  If the page was associated with a subpool, there
         * would have been a page reserved in the subpool before allocation
         * via hugepage_subpool_get_pages().  Since we are 'restoring' the
         * reservation, do not call hugepage_subpool_put_pages() as this will
         * remove the reserved page from the subpool.
         */
        if (!restore_reserve) {
                /*
                 * A return code of zero implies that the subpool will be
                 * under its minimum size if the reservation is not restored
                 * after page is free.  Therefore, force restore_reserve
                 * operation.
                 */
                if (hugepage_subpool_put_pages(spool, 1) == 0)
                        restore_reserve = true;
        }

        spin_lock_irqsave(&hugetlb_lock, flags);
        folio_clear_hugetlb_migratable(folio);
        hugetlb_cgroup_uncharge_folio(hstate_index(h),
                                     pages_per_huge_page(h), folio);
        hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
                                          pages_per_huge_page(h), folio);
        mem_cgroup_uncharge(folio);
        if (restore_reserve)
                h->resv_huge_pages++;

        if (folio_test_hugetlb_temporary(folio)) {
                remove_hugetlb_folio(h, folio, false);
                spin_unlock_irqrestore(&hugetlb_lock, flags);
                update_and_free_hugetlb_folio(h, folio, true);
        } else if (h->surplus_huge_pages_node[nid]) {
                /* remove the page from active list */
                remove_hugetlb_folio(h, folio, true);
                spin_unlock_irqrestore(&hugetlb_lock, flags);
                update_and_free_hugetlb_folio(h, folio, true);
        } else {
                arch_clear_hugetlb_flags(folio);
                enqueue_hugetlb_folio(h, folio);
                spin_unlock_irqrestore(&hugetlb_lock, flags);
        }
}

/*
 * Must be called with the hugetlb lock held
 */
static void __prep_account_new_huge_page(struct hstate *h, int nid)
{
        lockdep_assert_held(&hugetlb_lock);
        h->nr_huge_pages++;
        h->nr_huge_pages_node[nid]++;
}

static void init_new_hugetlb_folio(struct hstate *h, struct folio *folio)
{
        __folio_set_hugetlb(folio);
        INIT_LIST_HEAD(&folio->lru);
        hugetlb_set_folio_subpool(folio, NULL);
        set_hugetlb_cgroup(folio, NULL);
        set_hugetlb_cgroup_rsvd(folio, NULL);
}

static void __prep_new_hugetlb_folio(struct hstate *h, struct folio *folio)
{
        init_new_hugetlb_folio(h, folio);
        hugetlb_vmemmap_optimize_folio(h, folio);
}

static void prep_new_hugetlb_folio(struct hstate *h, struct folio *folio, int nid)
{
        __prep_new_hugetlb_folio(h, folio);
        spin_lock_irq(&hugetlb_lock);
        __prep_account_new_huge_page(h, nid);
        spin_unlock_irq(&hugetlb_lock);
}

static bool __prep_compound_gigantic_folio(struct folio *folio,
                                        unsigned int order, bool demote)
{
        int i, j;
        int nr_pages = 1 << order;
        struct page *p;

        __folio_clear_reserved(folio);
        for (i = 0; i < nr_pages; i++) {
                p = folio_page(folio, i);

                /*
                 * For gigantic hugepages allocated through bootmem at
                 * boot, it's safer to be consistent with the not-gigantic
                 * hugepages and clear the PG_reserved bit from all tail pages
                 * too.  Otherwise drivers using get_user_pages() to access tail
                 * pages may get the reference counting wrong if they see
                 * PG_reserved set on a tail page (despite the head page not
                 * having PG_reserved set).  Enforcing this consistency between
                 * head and tail pages allows drivers to optimize away a check
                 * on the head page when they need know if put_page() is needed
                 * after get_user_pages().
                 */
                if (i != 0)     /* head page cleared above */
                        __ClearPageReserved(p);
                /*
                 * Subtle and very unlikely
                 *
                 * Gigantic 'page allocators' such as memblock or cma will
                 * return a set of pages with each page ref counted.  We need
                 * to turn this set of pages into a compound page with tail
                 * page ref counts set to zero.  Code such as speculative page
                 * cache adding could take a ref on a 'to be' tail page.
                 * We need to respect any increased ref count, and only set
                 * the ref count to zero if count is currently 1.  If count
                 * is not 1, we return an error.  An error return indicates
                 * the set of pages can not be converted to a gigantic page.
                 * The caller who allocated the pages should then discard the
                 * pages using the appropriate free interface.
                 *
                 * In the case of demote, the ref count will be zero.
                 */
                if (!demote) {
                        if (!page_ref_freeze(p, 1)) {
                                pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
                                goto out_error;
                        }
                } else {
                        VM_BUG_ON_PAGE(page_count(p), p);
                }
                if (i != 0)
                        set_compound_head(p, &folio->page);
        }
        __folio_set_head(folio);
        /* we rely on prep_new_hugetlb_folio to set the hugetlb flag */
        folio_set_order(folio, order);
        atomic_set(&folio->_entire_mapcount, -1);
        atomic_set(&folio->_large_mapcount, -1);
        atomic_set(&folio->_pincount, 0);
        return true;

out_error:
        /* undo page modifications made above */
        for (j = 0; j < i; j++) {
                p = folio_page(folio, j);
                if (j != 0)
                        clear_compound_head(p);
                set_page_refcounted(p);
        }
        /* need to clear PG_reserved on remaining tail pages  */
        for (; j < nr_pages; j++) {
                p = folio_page(folio, j);
                __ClearPageReserved(p);
        }
        return false;
}

static bool prep_compound_gigantic_folio(struct folio *folio,
                                                        unsigned int order)
{
        return __prep_compound_gigantic_folio(folio, order, false);
}

static bool prep_compound_gigantic_folio_for_demote(struct folio *folio,
                                                        unsigned int order)
{
        return __prep_compound_gigantic_folio(folio, order, true);
}

/*
 * Find and lock address space (mapping) in write mode.
 *
 * Upon entry, the page is locked which means that page_mapping() is
 * stable.  Due to locking order, we can only trylock_write.  If we can
 * not get the lock, simply return NULL to caller.
 */
struct address_space *hugetlb_page_mapping_lock_write(struct page *hpage)
{
        struct address_space *mapping = page_mapping(hpage);

        if (!mapping)
                return mapping;

        if (i_mmap_trylock_write(mapping))
                return mapping;

        return NULL;
}

static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
                gfp_t gfp_mask, int nid, nodemask_t *nmask,
                nodemask_t *node_alloc_noretry)
{
        int order = huge_page_order(h);
        struct folio *folio;
        bool alloc_try_hard = true;
        bool retry = true;

        /*
         * By default we always try hard to allocate the folio with
         * __GFP_RETRY_MAYFAIL flag.  However, if we are allocating folios in
         * a loop (to adjust global huge page counts) and previous allocation
         * failed, do not continue to try hard on the same node.  Use the
         * node_alloc_noretry bitmap to manage this state information.
         */
        if (node_alloc_noretry && node_isset(nid, *node_alloc_noretry))
                alloc_try_hard = false;
        gfp_mask |= __GFP_COMP|__GFP_NOWARN;
        if (alloc_try_hard)
                gfp_mask |= __GFP_RETRY_MAYFAIL;
        if (nid == NUMA_NO_NODE)
                nid = numa_mem_id();
retry:
        folio = __folio_alloc(gfp_mask, order, nid, nmask);

        if (folio && !folio_ref_freeze(folio, 1)) {
                folio_put(folio);
                if (retry) {    /* retry once */
                        retry = false;
                        goto retry;
                }
                /* WOW!  twice in a row. */
                pr_warn("HugeTLB unexpected inflated folio ref count\n");
                folio = NULL;
        }

        /*
         * If we did not specify __GFP_RETRY_MAYFAIL, but still got a
         * folio this indicates an overall state change.  Clear bit so
         * that we resume normal 'try hard' allocations.
         */
        if (node_alloc_noretry && folio && !alloc_try_hard)
                node_clear(nid, *node_alloc_noretry);

        /*
         * If we tried hard to get a folio but failed, set bit so that
         * subsequent attempts will not try as hard until there is an
         * overall state change.
         */
        if (node_alloc_noretry && !folio && alloc_try_hard)
                node_set(nid, *node_alloc_noretry);

        if (!folio) {
                __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
                return NULL;
        }

        __count_vm_event(HTLB_BUDDY_PGALLOC);
        return folio;
}

static struct folio *__alloc_fresh_hugetlb_folio(struct hstate *h,
                                gfp_t gfp_mask, int nid, nodemask_t *nmask,
                                nodemask_t *node_alloc_noretry)
{
        struct folio *folio;
        bool retry = false;

retry:
        if (hstate_is_gigantic(h))
                folio = alloc_gigantic_folio(h, gfp_mask, nid, nmask);
        else
                folio = alloc_buddy_hugetlb_folio(h, gfp_mask,
                                nid, nmask, node_alloc_noretry);
        if (!folio)
                return NULL;

        if (hstate_is_gigantic(h)) {
                if (!prep_compound_gigantic_folio(folio, huge_page_order(h))) {
                        /*
                         * Rare failure to convert pages to compound page.
                         * Free pages and try again - ONCE!
                         */
                        free_gigantic_folio(folio, huge_page_order(h));
                        if (!retry) {
                                retry = true;
                                goto retry;
                        }
                        return NULL;
                }
        }

        return folio;
}

static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
                gfp_t gfp_mask, int nid, nodemask_t *nmask,
                nodemask_t *node_alloc_noretry)
{
        struct folio *folio;

        folio = __alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask,
                                                node_alloc_noretry);
        if (folio)
                init_new_hugetlb_folio(h, folio);
        return folio;
}

/*
 * Common helper to allocate a fresh hugetlb page. All specific allocators
 * should use this function to get new hugetlb pages
 *
 * Note that returned page is 'frozen':  ref count of head page and all tail
 * pages is zero.
 */
static struct folio *alloc_fresh_hugetlb_folio(struct hstate *h,
                gfp_t gfp_mask, int nid, nodemask_t *nmask,
                nodemask_t *node_alloc_noretry)
{
        struct folio *folio;

        folio = __alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask,
                                                node_alloc_noretry);
        if (!folio)
                return NULL;

        prep_new_hugetlb_folio(h, folio, folio_nid(folio));
        return folio;
}

static void prep_and_add_allocated_folios(struct hstate *h,
                                        struct list_head *folio_list)
{
        unsigned long flags;
        struct folio *folio, *tmp_f;

        /* Send list for bulk vmemmap optimization processing */
        hugetlb_vmemmap_optimize_folios(h, folio_list);

        /* Add all new pool pages to free lists in one lock cycle */
        spin_lock_irqsave(&hugetlb_lock, flags);
        list_for_each_entry_safe(folio, tmp_f, folio_list, lru) {
                __prep_account_new_huge_page(h, folio_nid(folio));
                enqueue_hugetlb_folio(h, folio);
        }
        spin_unlock_irqrestore(&hugetlb_lock, flags);
}

/*
 * Allocates a fresh hugetlb page in a node interleaved manner.  The page
 * will later be added to the appropriate hugetlb pool.
 */
static struct folio *alloc_pool_huge_folio(struct hstate *h,
                                        nodemask_t *nodes_allowed,
                                        nodemask_t *node_alloc_noretry,
                                        int *next_node)
{
        gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
        int nr_nodes, node;

        for_each_node_mask_to_alloc(next_node, nr_nodes, node, nodes_allowed) {
                struct folio *folio;

                folio = only_alloc_fresh_hugetlb_folio(h, gfp_mask, node,
                                        nodes_allowed, node_alloc_noretry);
                if (folio)
                        return folio;
        }

        return NULL;
}

/*
 * Remove huge page from pool from next node to free.  Attempt to keep
 * persistent huge pages more or less balanced over allowed nodes.
 * This routine only 'removes' the hugetlb page.  The caller must make
 * an additional call to free the page to low level allocators.
 * Called with hugetlb_lock locked.
 */
static struct folio *remove_pool_hugetlb_folio(struct hstate *h,
                nodemask_t *nodes_allowed, bool acct_surplus)
{
        int nr_nodes, node;
        struct folio *folio = NULL;

        lockdep_assert_held(&hugetlb_lock);
        for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
                /*
                 * If we're returning unused surplus pages, only examine
                 * nodes with surplus pages.
                 */
                if ((!acct_surplus || h->surplus_huge_pages_node[node]) &&
                    !list_empty(&h->hugepage_freelists[node])) {
                        folio = list_entry(h->hugepage_freelists[node].next,
                                          struct folio, lru);
                        remove_hugetlb_folio(h, folio, acct_surplus);
                        break;
                }
        }

        return folio;
}

/*
 * Dissolve a given free hugetlb folio into free buddy pages. This function
 * does nothing for in-use hugetlb folios and non-hugetlb folios.
 * This function returns values like below:
 *
 *  -ENOMEM: failed to allocate vmemmap pages to free the freed hugepages
 *           when the system is under memory pressure and the feature of
 *           freeing unused vmemmap pages associated with each hugetlb page
 *           is enabled.
 *  -EBUSY:  failed to dissolved free hugepages or the hugepage is in-use
 *           (allocated or reserved.)
 *       0:  successfully dissolved free hugepages or the page is not a
 *           hugepage (considered as already dissolved)
 */
int dissolve_free_hugetlb_folio(struct folio *folio)
{
        int rc = -EBUSY;

retry:
        /* Not to disrupt normal path by vainly holding hugetlb_lock */
        if (!folio_test_hugetlb(folio))
                return 0;

        spin_lock_irq(&hugetlb_lock);
        if (!folio_test_hugetlb(folio)) {
                rc = 0;
                goto out;
        }

        if (!folio_ref_count(folio)) {
                struct hstate *h = folio_hstate(folio);
                if (!available_huge_pages(h))
                        goto out;

                /*
                 * We should make sure that the page is already on the free list
                 * when it is dissolved.
                 */
                if (unlikely(!folio_test_hugetlb_freed(folio))) {
                        spin_unlock_irq(&hugetlb_lock);
                        cond_resched();

                        /*
                         * Theoretically, we should return -EBUSY when we
                         * encounter this race. In fact, we have a chance
                         * to successfully dissolve the page if we do a
                         * retry. Because the race window is quite small.
                         * If we seize this opportunity, it is an optimization
                         * for increasing the success rate of dissolving page.
                         */
                        goto retry;
                }

                remove_hugetlb_folio(h, folio, false);
                h->max_huge_pages--;
                spin_unlock_irq(&hugetlb_lock);

                /*
                 * Normally update_and_free_hugtlb_folio will allocate required vmemmmap
                 * before freeing the page.  update_and_free_hugtlb_folio will fail to
                 * free the page if it can not allocate required vmemmap.  We
                 * need to adjust max_huge_pages if the page is not freed.
                 * Attempt to allocate vmemmmap here so that we can take
                 * appropriate action on failure.
                 *
                 * The folio_test_hugetlb check here is because
                 * remove_hugetlb_folio will clear hugetlb folio flag for
                 * non-vmemmap optimized hugetlb folios.
                 */
                if (folio_test_hugetlb(folio)) {
                        rc = hugetlb_vmemmap_restore_folio(h, folio);
                        if (rc) {
                                spin_lock_irq(&hugetlb_lock);
                                add_hugetlb_folio(h, folio, false);
                                h->max_huge_pages++;
                                goto out;
                        }
                } else
                        rc = 0;

                update_and_free_hugetlb_folio(h, folio, false);
                return rc;
        }
out:
        spin_unlock_irq(&hugetlb_lock);
        return rc;
}

/*
 * Dissolve free hugepages in a given pfn range. Used by memory hotplug to
 * make specified memory blocks removable from the system.
 * Note that this will dissolve a free gigantic hugepage completely, if any
 * part of it lies within the given range.
 * Also note that if dissolve_free_hugetlb_folio() returns with an error, all
 * free hugetlb folios that were dissolved before that error are lost.
 */
int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
{
        unsigned long pfn;
        struct folio *folio;
        int rc = 0;
        unsigned int order;
        struct hstate *h;

        if (!hugepages_supported())
                return rc;

        order = huge_page_order(&default_hstate);
        for_each_hstate(h)
                order = min(order, huge_page_order(h));

        for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order) {
                folio = pfn_folio(pfn);
                rc = dissolve_free_hugetlb_folio(folio);
                if (rc)
                        break;
        }

        return rc;
}

/*
 * Allocates a fresh surplus page from the page allocator.
 */
static struct folio *alloc_surplus_hugetlb_folio(struct hstate *h,
                                gfp_t gfp_mask, int nid, nodemask_t *nmask)
{
        struct folio *folio = NULL;

        if (hstate_is_gigantic(h))
                return NULL;

        spin_lock_irq(&hugetlb_lock);
        if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages)
                goto out_unlock;
        spin_unlock_irq(&hugetlb_lock);

        folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
        if (!folio)
                return NULL;

        spin_lock_irq(&hugetlb_lock);
        /*
         * We could have raced with the pool size change.
         * Double check that and simply deallocate the new page
         * if we would end up overcommiting the surpluses. Abuse
         * temporary page to workaround the nasty free_huge_folio
         * codeflow
         */
        if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
                folio_set_hugetlb_temporary(folio);
                spin_unlock_irq(&hugetlb_lock);
                free_huge_folio(folio);
                return NULL;
        }

        h->surplus_huge_pages++;
        h->surplus_huge_pages_node[folio_nid(folio)]++;

out_unlock:
        spin_unlock_irq(&hugetlb_lock);

        return folio;
}

static struct folio *alloc_migrate_hugetlb_folio(struct hstate *h, gfp_t gfp_mask,
                                     int nid, nodemask_t *nmask)
{
        struct folio *folio;

        if (hstate_is_gigantic(h))
                return NULL;

        folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid, nmask, NULL);
        if (!folio)
                return NULL;

        /* fresh huge pages are frozen */
        folio_ref_unfreeze(folio, 1);
        /*
         * We do not account these pages as surplus because they are only
         * temporary and will be released properly on the last reference
         */
        folio_set_hugetlb_temporary(folio);

        return folio;
}

/*
 * Use the VMA's mpolicy to allocate a huge page from the buddy.
 */
static
struct folio *alloc_buddy_hugetlb_folio_with_mpol(struct hstate *h,
                struct vm_area_struct *vma, unsigned long addr)
{
        struct folio *folio = NULL;
        struct mempolicy *mpol;
        gfp_t gfp_mask = htlb_alloc_mask(h);
        int nid;
        nodemask_t *nodemask;

        nid = huge_node(vma, addr, gfp_mask, &mpol, &nodemask);
        if (mpol_is_preferred_many(mpol)) {
                gfp_t gfp = gfp_mask | __GFP_NOWARN;

                gfp &=  ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
                folio = alloc_surplus_hugetlb_folio(h, gfp, nid, nodemask);

                /* Fallback to all nodes if page==NULL */
                nodemask = NULL;
        }

        if (!folio)
                folio = alloc_surplus_hugetlb_folio(h, gfp_mask, nid, nodemask);
        mpol_cond_put(mpol);
        return folio;
}

/* folio migration callback function */
struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
                nodemask_t *nmask, gfp_t gfp_mask, bool allow_alloc_fallback)
{
        spin_lock_irq(&hugetlb_lock);
        if (available_huge_pages(h)) {
                struct folio *folio;

                folio = dequeue_hugetlb_folio_nodemask(h, gfp_mask,
                                                preferred_nid, nmask);
                if (folio) {
                        spin_unlock_irq(&hugetlb_lock);
                        return folio;
                }
        }
        spin_unlock_irq(&hugetlb_lock);

        /* We cannot fallback to other nodes, as we could break the per-node pool. */
        if (!allow_alloc_fallback)
                gfp_mask |= __GFP_THISNODE;

        return alloc_migrate_hugetlb_folio(h, gfp_mask, preferred_nid, nmask);
}

/*
 * Increase the hugetlb pool such that it can accommodate a reservation
 * of size 'delta'.
 */
static int gather_surplus_pages(struct hstate *h, long delta)
        __must_hold(&hugetlb_lock)
{
        LIST_HEAD(surplus_list);
        struct folio *folio, *tmp;
        int ret;
        long i;
        long needed, allocated;
        bool alloc_ok = true;

        lockdep_assert_held(&hugetlb_lock);
        needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
        if (needed <= 0) {
                h->resv_huge_pages += delta;
                return 0;
        }

        allocated = 0;

        ret = -ENOMEM;
retry:
        spin_unlock_irq(&hugetlb_lock);
        for (i = 0; i < needed; i++) {
                folio = alloc_surplus_hugetlb_folio(h, htlb_alloc_mask(h),
                                NUMA_NO_NODE, NULL);
                if (!folio) {
                        alloc_ok = false;
                        break;
                }
                list_add(&folio->lru, &surplus_list);
                cond_resched();
        }
        allocated += i;

        /*
         * After retaking hugetlb_lock, we need to recalculate 'needed'
         * because either resv_huge_pages or free_huge_pages may have changed.
         */
        spin_lock_irq(&hugetlb_lock);
        needed = (h->resv_huge_pages + delta) -
                        (h->free_huge_pages + allocated);
        if (needed > 0) {
                if (alloc_ok)
                        goto retry;
                /*
                 * We were not able to allocate enough pages to
                 * satisfy the entire reservation so we free what
                 * we've allocated so far.
                 */
                goto free;
        }
        /*
         * The surplus_list now contains _at_least_ the number of extra pages
         * needed to accommodate the reservation.  Add the appropriate number
         * of pages to the hugetlb pool and free the extras back to the buddy
         * allocator.  Commit the entire reservation here to prevent another
         * process from stealing the pages as they are added to the pool but
         * before they are reserved.
         */
        needed += allocated;
        h->resv_huge_pages += delta;
        ret = 0;

        /* Free the needed pages to the hugetlb pool */
        list_for_each_entry_safe(folio, tmp, &surplus_list, lru) {
                if ((--needed) < 0)
                        break;
                /* Add the page to the hugetlb allocator */
                enqueue_hugetlb_folio(h, folio);
        }
free:
        spin_unlock_irq(&hugetlb_lock);

        /*
         * Free unnecessary surplus pages to the buddy allocator.
         * Pages have no ref count, call free_huge_folio directly.
         */
        list_for_each_entry_safe(folio, tmp, &surplus_list, lru)
                free_huge_folio(folio);
        spin_lock_irq(&hugetlb_lock);

        return ret;
}

/*
 * This routine has two main purposes:
 * 1) Decrement the reservation count (resv_huge_pages) by the value passed
 *    in unused_resv_pages.  This corresponds to the prior adjustments made
 *    to the associated reservation map.
 * 2) Free any unused surplus pages that may have been allocated to satisfy
 *    the reservation.  As many as unused_resv_pages may be freed.
 */
static void return_unused_surplus_pages(struct hstate *h,
                                        unsigned long unused_resv_pages)
{
        unsigned long nr_pages;
        LIST_HEAD(page_list);

        lockdep_assert_held(&hugetlb_lock);
        /* Uncommit the reservation */
        h->resv_huge_pages -= unused_resv_pages;

        if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                goto out;

        /*
         * Part (or even all) of the reservation could have been backed
         * by pre-allocated pages. Only free surplus pages.
         */
        nr_pages = min(unused_resv_pages, h->surplus_huge_pages);

        /*
         * We want to release as many surplus pages as possible, spread
         * evenly across all nodes with memory. Iterate across these nodes
         * until we can no longer free unreserved surplus pages. This occurs
         * when the nodes with surplus pages have no free pages.
         * remove_pool_hugetlb_folio() will balance the freed pages across the
         * on-line nodes with memory and will handle the hstate accounting.
         */
        while (nr_pages--) {
                struct folio *folio;

                folio = remove_pool_hugetlb_folio(h, &node_states[N_MEMORY], 1);
                if (!folio)
                        goto out;

                list_add(&folio->lru, &page_list);
        }

out:
        spin_unlock_irq(&hugetlb_lock);
        update_and_free_pages_bulk(h, &page_list);
        spin_lock_irq(&hugetlb_lock);
}


/*
 * vma_needs_reservation, vma_commit_reservation and vma_end_reservation
 * are used by the huge page allocation routines to manage reservations.
 *
 * vma_needs_reservation is called to determine if the huge page at addr
 * within the vma has an associated reservation.  If a reservation is
 * needed, the value 1 is returned.  The caller is then responsible for
 * managing the global reservation and subpool usage counts.  After
 * the huge page has been allocated, vma_commit_reservation is called
 * to add the page to the reservation map.  If the page allocation fails,
 * the reservation must be ended instead of committed.  vma_end_reservation
 * is called in such cases.
 *
 * In the normal case, vma_commit_reservation returns the same value
 * as the preceding vma_needs_reservation call.  The only time this
 * is not the case is if a reserve map was changed between calls.  It
 * is the responsibility of the caller to notice the difference and
 * take appropriate action.
 *
 * vma_add_reservation is used in error paths where a reservation must
 * be restored when a newly allocated huge page must be freed.  It is
 * to be called after calling vma_needs_reservation to determine if a
 * reservation exists.
 *
 * vma_del_reservation is used in error paths where an entry in the reserve
 * map was created during huge page allocation and must be removed.  It is to
 * be called after calling vma_needs_reservation to determine if a reservation
 * exists.
 */
enum vma_resv_mode {
        VMA_NEEDS_RESV,
        VMA_COMMIT_RESV,
        VMA_END_RESV,
        VMA_ADD_RESV,
        VMA_DEL_RESV,
};
static long __vma_reservation_common(struct hstate *h,
                                struct vm_area_struct *vma, unsigned long addr,
                                enum vma_resv_mode mode)
{
        struct resv_map *resv;
        pgoff_t idx;
        long ret;
        long dummy_out_regions_needed;

        resv = vma_resv_map(vma);
        if (!resv)
                return 1;

        idx = vma_hugecache_offset(h, vma, addr);
        switch (mode) {
        case VMA_NEEDS_RESV:
                ret = region_chg(resv, idx, idx + 1, &dummy_out_regions_needed);
                /* We assume that vma_reservation_* routines always operate on
                 * 1 page, and that adding to resv map a 1 page entry can only
                 * ever require 1 region.
                 */
                VM_BUG_ON(dummy_out_regions_needed != 1);
                break;
        case VMA_COMMIT_RESV:
                ret = region_add(resv, idx, idx + 1, 1, NULL, NULL);
                /* region_add calls of range 1 should never fail. */
                VM_BUG_ON(ret < 0);
                break;
        case VMA_END_RESV:
                region_abort(resv, idx, idx + 1, 1);
                ret = 0;
                break;
        case VMA_ADD_RESV:
                if (vma->vm_flags & VM_MAYSHARE) {
                        ret = region_add(resv, idx, idx + 1, 1, NULL, NULL);
                        /* region_add calls of range 1 should never fail. */
                        VM_BUG_ON(ret < 0);
                } else {
                        region_abort(resv, idx, idx + 1, 1);
                        ret = region_del(resv, idx, idx + 1);
                }
                break;
        case VMA_DEL_RESV:
                if (vma->vm_flags & VM_MAYSHARE) {
                        region_abort(resv, idx, idx + 1, 1);
                        ret = region_del(resv, idx, idx + 1);
                } else {
                        ret = region_add(resv, idx, idx + 1, 1, NULL, NULL);
                        /* region_add calls of range 1 should never fail. */
                        VM_BUG_ON(ret < 0);
                }
                break;
        default:
                BUG();
        }

        if (vma->vm_flags & VM_MAYSHARE || mode == VMA_DEL_RESV)
                return ret;
        /*
         * We know private mapping must have HPAGE_RESV_OWNER set.
         *
         * In most cases, reserves always exist for private mappings.
         * However, a file associated with mapping could have been
         * hole punched or truncated after reserves were consumed.
         * As subsequent fault on such a range will not use reserves.
         * Subtle - The reserve map for private mappings has the
         * opposite meaning than that of shared mappings.  If NO
         * entry is in the reserve map, it means a reservation exists.
         * If an entry exists in the reserve map, it means the
         * reservation has already been consumed.  As a result, the
         * return value of this routine is the opposite of the
         * value returned from reserve map manipulation routines above.
         */
        if (ret > 0)
                return 0;
        if (ret == 0)
                return 1;
        return ret;
}

static long vma_needs_reservation(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long addr)
{
        return __vma_reservation_common(h, vma, addr, VMA_NEEDS_RESV);
}

static long vma_commit_reservation(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long addr)
{
        return __vma_reservation_common(h, vma, addr, VMA_COMMIT_RESV);
}

static void vma_end_reservation(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long addr)
{
        (void)__vma_reservation_common(h, vma, addr, VMA_END_RESV);
}

static long vma_add_reservation(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long addr)
{
        return __vma_reservation_common(h, vma, addr, VMA_ADD_RESV);
}

static long vma_del_reservation(struct hstate *h,
                        struct vm_area_struct *vma, unsigned long addr)
{
        return __vma_reservation_common(h, vma, addr, VMA_DEL_RESV);
}

/*
 * This routine is called to restore reservation information on error paths.
 * It should ONLY be called for folios allocated via alloc_hugetlb_folio(),
 * and the hugetlb mutex should remain held when calling this routine.
 *
 * It handles two specific cases:
 * 1) A reservation was in place and the folio consumed the reservation.
 *    hugetlb_restore_reserve is set in the folio.
 * 2) No reservation was in place for the page, so hugetlb_restore_reserve is
 *    not set.  However, alloc_hugetlb_folio always updates the reserve map.
 *
 * In case 1, free_huge_folio later in the error path will increment the
 * global reserve count.  But, free_huge_folio does not have enough context
 * to adjust the reservation map.  This case deals primarily with private
 * mappings.  Adjust the reserve map here to be consistent with global
 * reserve count adjustments to be made by free_huge_folio.  Make sure the
 * reserve map indicates there is a reservation present.
 *
 * In case 2, simply undo reserve map modifications done by alloc_hugetlb_folio.
 */
void restore_reserve_on_error(struct hstate *h, struct vm_area_struct *vma,
                        unsigned long address, struct folio *folio)
{
        long rc = vma_needs_reservation(h, vma, address);

        if (folio_test_hugetlb_restore_reserve(folio)) {
                if (unlikely(rc < 0))
                        /*
                         * Rare out of memory condition in reserve map
                         * manipulation.  Clear hugetlb_restore_reserve so
                         * that global reserve count will not be incremented
                         * by free_huge_folio.  This will make it appear
                         * as though the reservation for this folio was
                         * consumed.  This may prevent the task from
                         * faulting in the folio at a later time.  This
                         * is better than inconsistent global huge page
                         * accounting of reserve counts.
                         */
                        folio_clear_hugetlb_restore_reserve(folio);
                else if (rc)
                        (void)vma_add_reservation(h, vma, address);
                else
                        vma_end_reservation(h, vma, address);
        } else {
                if (!rc) {
                        /*
                         * This indicates there is an entry in the reserve map
                         * not added by alloc_hugetlb_folio.  We know it was added
                         * before the alloc_hugetlb_folio call, otherwise
                         * hugetlb_restore_reserve would be set on the folio.
                         * Remove the entry so that a subsequent allocation
                         * does not consume a reservation.
                         */
                        rc = vma_del_reservation(h, vma, address);
                        if (rc < 0)
                                /*
                                 * VERY rare out of memory condition.  Since
                                 * we can not delete the entry, set
                                 * hugetlb_restore_reserve so that the reserve
                                 * count will be incremented when the folio
                                 * is freed.  This reserve will be consumed
                                 * on a subsequent allocation.
                                 */
                                folio_set_hugetlb_restore_reserve(folio);
                } else if (rc < 0) {
                        /*
                         * Rare out of memory condition from
                         * vma_needs_reservation call.  Memory allocation is
                         * only attempted if a new entry is needed.  Therefore,
                         * this implies there is not an entry in the
                         * reserve map.
                         *
                         * For shared mappings, no entry in the map indicates
                         * no reservation.  We are done.
                         */
                        if (!(vma->vm_flags & VM_MAYSHARE))
                                /*
                                 * For private mappings, no entry indicates
                                 * a reservation is present.  Since we can
                                 * not add an entry, set hugetlb_restore_reserve
                                 * on the folio so reserve count will be
                                 * incremented when freed.  This reserve will
                                 * be consumed on a subsequent allocation.
                                 */
                                folio_set_hugetlb_restore_reserve(folio);
                } else
                        /*
                         * No reservation present, do nothing
                         */
                         vma_end_reservation(h, vma, address);
        }
}

/*
 * alloc_and_dissolve_hugetlb_folio - Allocate a new folio and dissolve
 * the old one
 * @h: struct hstate old page belongs to
 * @old_folio: Old folio to dissolve
 * @list: List to isolate the page in case we need to
 * Returns 0 on success, otherwise negated error.
 */
static int alloc_and_dissolve_hugetlb_folio(struct hstate *h,
                        struct folio *old_folio, struct list_head *list)
{
        gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
        int nid = folio_nid(old_folio);
        struct folio *new_folio = NULL;
        int ret = 0;

retry:
        spin_lock_irq(&hugetlb_lock);
        if (!folio_test_hugetlb(old_folio)) {
                /*
                 * Freed from under us. Drop new_folio too.
                 */
                goto free_new;
        } else if (folio_ref_count(old_folio)) {
                bool isolated;

                /*
                 * Someone has grabbed the folio, try to isolate it here.
                 * Fail with -EBUSY if not possible.
                 */
                spin_unlock_irq(&hugetlb_lock);
                isolated = isolate_hugetlb(old_folio, list);
                ret = isolated ? 0 : -EBUSY;
                spin_lock_irq(&hugetlb_lock);
                goto free_new;
        } else if (!folio_test_hugetlb_freed(old_folio)) {
                /*
                 * Folio's refcount is 0 but it has not been enqueued in the
                 * freelist yet. Race window is small, so we can succeed here if
                 * we retry.
                 */
                spin_unlock_irq(&hugetlb_lock);
                cond_resched();
                goto retry;
        } else {
                if (!new_folio) {
                        spin_unlock_irq(&hugetlb_lock);
                        new_folio = alloc_buddy_hugetlb_folio(h, gfp_mask, nid,
                                                              NULL, NULL);
                        if (!new_folio)
                                return -ENOMEM;
                        __prep_new_hugetlb_folio(h, new_folio);
                        goto retry;
                }

                /*
                 * Ok, old_folio is still a genuine free hugepage. Remove it from
                 * the freelist and decrease the counters. These will be
                 * incremented again when calling __prep_account_new_huge_page()
                 * and enqueue_hugetlb_folio() for new_folio. The counters will
                 * remain stable since this happens under the lock.
                 */
                remove_hugetlb_folio(h, old_folio, false);

                /*
                 * Ref count on new_folio is already zero as it was dropped
                 * earlier.  It can be directly added to the pool free list.
                 */
                __prep_account_new_huge_page(h, nid);
                enqueue_hugetlb_folio(h, new_folio);

                /*
                 * Folio has been replaced, we can safely free the old one.
                 */
                spin_unlock_irq(&hugetlb_lock);
                update_and_free_hugetlb_folio(h, old_folio, false);
        }

        return ret;

free_new:
        spin_unlock_irq(&hugetlb_lock);
        if (new_folio) {
                /* Folio has a zero ref count, but needs a ref to be freed */
                folio_ref_unfreeze(new_folio, 1);
                update_and_free_hugetlb_folio(h, new_folio, false);
        }

        return ret;
}

int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
{
        struct hstate *h;
        struct folio *folio = page_folio(page);
        int ret = -EBUSY;

        /*
         * The page might have been dissolved from under our feet, so make sure
         * to carefully check the state under the lock.
         * Return success when racing as if we dissolved the page ourselves.
         */
        spin_lock_irq(&hugetlb_lock);
        if (folio_test_hugetlb(folio)) {
                h = folio_hstate(folio);
        } else {
                spin_unlock_irq(&hugetlb_lock);
                return 0;
        }
        spin_unlock_irq(&hugetlb_lock);

        /*
         * Fence off gigantic pages as there is a cyclic dependency between
         * alloc_contig_range and them. Return -ENOMEM as this has the effect
         * of bailing out right away without further retrying.
         */
        if (hstate_is_gigantic(h))
                return -ENOMEM;

        if (folio_ref_count(folio) && isolate_hugetlb(folio, list))
                ret = 0;
        else if (!folio_ref_count(folio))
                ret = alloc_and_dissolve_hugetlb_folio(h, folio, list);

        return ret;
}

struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
                                    unsigned long addr, int avoid_reserve)
{
        struct hugepage_subpool *spool = subpool_vma(vma);
        struct hstate *h = hstate_vma(vma);
        struct folio *folio;
        long map_chg, map_commit, nr_pages = pages_per_huge_page(h);
        long gbl_chg;
        int memcg_charge_ret, ret, idx;
        struct hugetlb_cgroup *h_cg = NULL;
        struct mem_cgroup *memcg;
        bool deferred_reserve;
        gfp_t gfp = htlb_alloc_mask(h) | __GFP_RETRY_MAYFAIL;

        memcg = get_mem_cgroup_from_current();
        memcg_charge_ret = mem_cgroup_hugetlb_try_charge(memcg, gfp, nr_pages);
        if (memcg_charge_ret == -ENOMEM) {
                mem_cgroup_put(memcg);
                return ERR_PTR(-ENOMEM);
        }

        idx = hstate_index(h);
        /*
         * Examine the region/reserve map to determine if the process
         * has a reservation for the page to be allocated.  A return
         * code of zero indicates a reservation exists (no change).
         */
        map_chg = gbl_chg = vma_needs_reservation(h, vma, addr);
        if (map_chg < 0) {
                if (!memcg_charge_ret)
                        mem_cgroup_cancel_charge(memcg, nr_pages);
                mem_cgroup_put(memcg);
                return ERR_PTR(-ENOMEM);
        }

        /*
         * Processes that did not create the mapping will have no
         * reserves as indicated by the region/reserve map. Check
         * that the allocation will not exceed the subpool limit.
         * Allocations for MAP_NORESERVE mappings also need to be
         * checked against any subpool limit.
         */
        if (map_chg || avoid_reserve) {
                gbl_chg = hugepage_subpool_get_pages(spool, 1);
                if (gbl_chg < 0)
                        goto out_end_reservation;

                /*
                 * Even though there was no reservation in the region/reserve
                 * map, there could be reservations associated with the
                 * subpool that can be used.  This would be indicated if the
                 * return value of hugepage_subpool_get_pages() is zero.
                 * However, if avoid_reserve is specified we still avoid even
                 * the subpool reservations.
                 */
                if (avoid_reserve)
                        gbl_chg = 1;
        }

        /* If this allocation is not consuming a reservation, charge it now.
         */
        deferred_reserve = map_chg || avoid_reserve;
        if (deferred_reserve) {
                ret = hugetlb_cgroup_charge_cgroup_rsvd(
                        idx, pages_per_huge_page(h), &h_cg);
                if (ret)
                        goto out_subpool_put;
        }

        ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
        if (ret)
                goto out_uncharge_cgroup_reservation;

        spin_lock_irq(&hugetlb_lock);
        /*
         * glb_chg is passed to indicate whether or not a page must be taken
         * from the global free pool (global change).  gbl_chg == 0 indicates
         * a reservation exists for the allocation.
         */
        folio = dequeue_hugetlb_folio_vma(h, vma, addr, avoid_reserve, gbl_chg);
        if (!folio) {
                spin_unlock_irq(&hugetlb_lock);
                folio = alloc_buddy_hugetlb_folio_with_mpol(h, vma, addr);
                if (!folio)
                        goto out_uncharge_cgroup;
                spin_lock_irq(&hugetlb_lock);
                if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) {
                        folio_set_hugetlb_restore_reserve(folio);
                        h->resv_huge_pages--;
                }
                list_add(&folio->lru, &h->hugepage_activelist);
                folio_ref_unfreeze(folio, 1);
                /* Fall through */
        }

        hugetlb_cgroup_commit_charge(idx, pages_per_huge_page(h), h_cg, folio);
        /* If allocation is not consuming a reservation, also store the
         * hugetlb_cgroup pointer on the page.
         */
        if (deferred_reserve) {
                hugetlb_cgroup_commit_charge_rsvd(idx, pages_per_huge_page(h),
                                                  h_cg, folio);
        }

        spin_unlock_irq(&hugetlb_lock);

        hugetlb_set_folio_subpool(folio, spool);

        map_commit = vma_commit_reservation(h, vma, addr);
        if (unlikely(map_chg > map_commit)) {
                /*
                 * The page was added to the reservation map between
                 * vma_needs_reservation and vma_commit_reservation.
                 * This indicates a race with hugetlb_reserve_pages.
                 * Adjust for the subpool count incremented above AND
                 * in hugetlb_reserve_pages for the same page.  Also,
                 * the reservation count added in hugetlb_reserve_pages
                 * no longer applies.
                 */
                long rsv_adjust;

                rsv_adjust = hugepage_subpool_put_pages(spool, 1);
                hugetlb_acct_memory(h, -rsv_adjust);
                if (deferred_reserve) {
                        spin_lock_irq(&hugetlb_lock);
                        hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
                                        pages_per_huge_page(h), folio);
                        spin_unlock_irq(&hugetlb_lock);
                }
        }

        if (!memcg_charge_ret)
                mem_cgroup_commit_charge(folio, memcg);
        mem_cgroup_put(memcg);

        return folio;

out_uncharge_cgroup:
        hugetlb_cgroup_uncharge_cgroup(idx, pages_per_huge_page(h), h_cg);
out_uncharge_cgroup_reservation:
        if (deferred_reserve)
                hugetlb_cgroup_uncharge_cgroup_rsvd(idx, pages_per_huge_page(h),
                                                    h_cg);
out_subpool_put:
        if (map_chg || avoid_reserve)
                hugepage_subpool_put_pages(spool, 1);
out_end_reservation:
        vma_end_reservation(h, vma, addr);
        if (!memcg_charge_ret)
                mem_cgroup_cancel_charge(memcg, nr_pages);
        mem_cgroup_put(memcg);
        return ERR_PTR(-ENOSPC);
}

int alloc_bootmem_huge_page(struct hstate *h, int nid)
        __attribute__ ((weak, alias("__alloc_bootmem_huge_page")));
int __alloc_bootmem_huge_page(struct hstate *h, int nid)
{
        struct huge_bootmem_page *m = NULL; /* initialize for clang */
        int nr_nodes, node = nid;

        /* do node specific alloc */
        if (nid != NUMA_NO_NODE) {
                m = memblock_alloc_try_nid_raw(huge_page_size(h), huge_page_size(h),
                                0, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
                if (!m)
                        return 0;
                goto found;
        }
        /* allocate from next node when distributing huge pages */
        for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, &node_states[N_MEMORY]) {
                m = memblock_alloc_try_nid_raw(
                                huge_page_size(h), huge_page_size(h),
                                0, MEMBLOCK_ALLOC_ACCESSIBLE, node);
                /*
                 * Use the beginning of the huge page to store the
                 * huge_bootmem_page struct (until gather_bootmem
                 * puts them into the mem_map).
                 */
                if (!m)
                        return 0;
                goto found;
        }

found:

        /*
         * Only initialize the head struct page in memmap_init_reserved_pages,
         * rest of the struct pages will be initialized by the HugeTLB
         * subsystem itself.
         * The head struct page is used to get folio information by the HugeTLB
         * subsystem like zone id and node id.
         */
        memblock_reserved_mark_noinit(virt_to_phys((void *)m + PAGE_SIZE),
                huge_page_size(h) - PAGE_SIZE);
        /* Put them into a private list first because mem_map is not up yet */
        INIT_LIST_HEAD(&m->list);
        list_add(&m->list, &huge_boot_pages[node]);
        m->hstate = h;
        return 1;
}

/* Initialize [start_page:end_page_number] tail struct pages of a hugepage */
static void __init hugetlb_folio_init_tail_vmemmap(struct folio *folio,
                                        unsigned long start_page_number,
                                        unsigned long end_page_number)
{
        enum zone_type zone = zone_idx(folio_zone(folio));
        int nid = folio_nid(folio);
        unsigned long head_pfn = folio_pfn(folio);
        unsigned long pfn, end_pfn = head_pfn + end_page_number;
        int ret;

        for (pfn = head_pfn + start_page_number; pfn < end_pfn; pfn++) {
                struct page *page = pfn_to_page(pfn);

                __init_single_page(page, pfn, zone, nid);
                prep_compound_tail((struct page *)folio, pfn - head_pfn);
                ret = page_ref_freeze(page, 1);
                VM_BUG_ON(!ret);
        }
}

static void __init hugetlb_folio_init_vmemmap(struct folio *folio,
                                              struct hstate *h,
                                              unsigned long nr_pages)
{
        int ret;

        /* Prepare folio head */
        __folio_clear_reserved(folio);
        __folio_set_head(folio);
        ret = folio_ref_freeze(folio, 1);
        VM_BUG_ON(!ret);
        /* Initialize the necessary tail struct pages */
        hugetlb_folio_init_tail_vmemmap(folio, 1, nr_pages);
        prep_compound_head((struct page *)folio, huge_page_order(h));
}

static void __init prep_and_add_bootmem_folios(struct hstate *h,
                                        struct list_head *folio_list)
{
        unsigned long flags;
        struct folio *folio, *tmp_f;

        /* Send list for bulk vmemmap optimization processing */
        hugetlb_vmemmap_optimize_folios(h, folio_list);

        list_for_each_entry_safe(folio, tmp_f, folio_list, lru) {
                if (!folio_test_hugetlb_vmemmap_optimized(folio)) {
                        /*
                         * If HVO fails, initialize all tail struct pages
                         * We do not worry about potential long lock hold
                         * time as this is early in boot and there should
                         * be no contention.
                         */
                        hugetlb_folio_init_tail_vmemmap(folio,
                                        HUGETLB_VMEMMAP_RESERVE_PAGES,
                                        pages_per_huge_page(h));
                }
                /* Subdivide locks to achieve better parallel performance */
                spin_lock_irqsave(&hugetlb_lock, flags);
                __prep_account_new_huge_page(h, folio_nid(folio));
                enqueue_hugetlb_folio(h, folio);
                spin_unlock_irqrestore(&hugetlb_lock, flags);
        }
}

/*
 * Put bootmem huge pages into the standard lists after mem_map is up.
 * Note: This only applies to gigantic (order > MAX_PAGE_ORDER) pages.
 */
static void __init gather_bootmem_prealloc_node(unsigned long nid)
{
        LIST_HEAD(folio_list);
        struct huge_bootmem_page *m;
        struct hstate *h = NULL, *prev_h = NULL;

        list_for_each_entry(m, &huge_boot_pages[nid], list) {
                struct page *page = virt_to_page(m);
                struct folio *folio = (void *)page;

                h = m->hstate;
                /*
                 * It is possible to have multiple huge page sizes (hstates)
                 * in this list.  If so, process each size separately.
                 */
                if (h != prev_h && prev_h != NULL)
                        prep_and_add_bootmem_folios(prev_h, &folio_list);
                prev_h = h;

                VM_BUG_ON(!hstate_is_gigantic(h));
                WARN_ON(folio_ref_count(folio) != 1);

                hugetlb_folio_init_vmemmap(folio, h,
                                           HUGETLB_VMEMMAP_RESERVE_PAGES);
                init_new_hugetlb_folio(h, folio);
                list_add(&folio->lru, &folio_list);

                /*
                 * We need to restore the 'stolen' pages to totalram_pages
                 * in order to fix confusing memory reports from free(1) and
                 * other side-effects, like CommitLimit going negative.
                 */
                adjust_managed_page_count(page, pages_per_huge_page(h));
                cond_resched();
        }

        prep_and_add_bootmem_folios(h, &folio_list);
}

static void __init gather_bootmem_prealloc_parallel(unsigned long start,
                                                    unsigned long end, void *arg)
{
        int nid;

        for (nid = start; nid < end; nid++)
                gather_bootmem_prealloc_node(nid);
}

static void __init gather_bootmem_prealloc(void)
{
        struct padata_mt_job job = {
                .thread_fn      = gather_bootmem_prealloc_parallel,
                .fn_arg         = NULL,
                .start          = 0,
                .size           = num_node_state(N_MEMORY),
                .align          = 1,
                .min_chunk      = 1,
                .max_threads    = num_node_state(N_MEMORY),
                .numa_aware     = true,
        };

        padata_do_multithreaded(&job);
}

static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
{
        unsigned long i;
        char buf[32];

        for (i = 0; i < h->max_huge_pages_node[nid]; ++i) {
                if (hstate_is_gigantic(h)) {
                        if (!alloc_bootmem_huge_page(h, nid))
                                break;
                } else {
                        struct folio *folio;
                        gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;

                        folio = alloc_fresh_hugetlb_folio(h, gfp_mask, nid,
                                        &node_states[N_MEMORY], NULL);
                        if (!folio)
                                break;
                        free_huge_folio(folio); /* free it into the hugepage allocator */
                }
                cond_resched();
        }
        if (i == h->max_huge_pages_node[nid])
                return;

        string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
        pr_warn("HugeTLB: allocating %u of page size %s failed node%d.  Only allocated %lu hugepages.\n",
                h->max_huge_pages_node[nid], buf, nid, i);
        h->max_huge_pages -= (h->max_huge_pages_node[nid] - i);
        h->max_huge_pages_node[nid] = i;
}

static bool __init hugetlb_hstate_alloc_pages_specific_nodes(struct hstate *h)
{
        int i;
        bool node_specific_alloc = false;

        for_each_online_node(i) {
                if (h->max_huge_pages_node[i] > 0) {
                        hugetlb_hstate_alloc_pages_onenode(h, i);
                        node_specific_alloc = true;
                }
        }

        return node_specific_alloc;
}

static void __init hugetlb_hstate_alloc_pages_errcheck(unsigned long allocated, struct hstate *h)
{
        if (allocated < h->max_huge_pages) {
                char buf[32];

                string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
                pr_warn("HugeTLB: allocating %lu of page size %s failed.  Only allocated %lu hugepages.\n",
                        h->max_huge_pages, buf, allocated);
                h->max_huge_pages = allocated;
        }
}

static void __init hugetlb_pages_alloc_boot_node(unsigned long start, unsigned long end, void *arg)
{
        struct hstate *h = (struct hstate *)arg;
        int i, num = end - start;
        nodemask_t node_alloc_noretry;
        LIST_HEAD(folio_list);
        int next_node = first_online_node;

        /* Bit mask controlling how hard we retry per-node allocations.*/
        nodes_clear(node_alloc_noretry);

        for (i = 0; i < num; ++i) {
                struct folio *folio = alloc_pool_huge_folio(h, &node_states[N_MEMORY],
                                                &node_alloc_noretry, &next_node);
                if (!folio)
                        break;

                list_move(&folio->lru, &folio_list);
                cond_resched();
        }

        prep_and_add_allocated_folios(h, &folio_list);
}

static unsigned long __init hugetlb_gigantic_pages_alloc_boot(struct hstate *h)
{
        unsigned long i;

        for (i = 0; i < h->max_huge_pages; ++i) {
                if (!alloc_bootmem_huge_page(h, NUMA_NO_NODE))
                        break;
                cond_resched();
        }

        return i;
}

static unsigned long __init hugetlb_pages_alloc_boot(struct hstate *h)
{
        struct padata_mt_job job = {
                .fn_arg         = h,
                .align          = 1,
                .numa_aware     = true
        };

        job.thread_fn   = hugetlb_pages_alloc_boot_node;
        job.start       = 0;
        job.size        = h->max_huge_pages;

        /*
         * job.max_threads is twice the num_node_state(N_MEMORY),
         *
         * Tests below indicate that a multiplier of 2 significantly improves
         * performance, and although larger values also provide improvements,
         * the gains are marginal.
         *
         * Therefore, choosing 2 as the multiplier strikes a good balance between
         * enhancing parallel processing capabilities and maintaining efficient
         * resource management.
         *
         * +------------+-------+-------+-------+-------+-------+
         * | multiplier |   1   |   2   |   3   |   4   |   5   |
         * +------------+-------+-------+-------+-------+-------+
         * | 256G 2node | 358ms | 215ms | 157ms | 134ms | 126ms |
         * | 2T   4node | 979ms | 679ms | 543ms | 489ms | 481ms |
         * | 50G  2node | 71ms  | 44ms  | 37ms  | 30ms  | 31ms  |
         * +------------+-------+-------+-------+-------+-------+
         */
        job.max_threads = num_node_state(N_MEMORY) * 2;
        job.min_chunk   = h->max_huge_pages / num_node_state(N_MEMORY) / 2;
        padata_do_multithreaded(&job);

        return h->nr_huge_pages;
}

/*
 * NOTE: this routine is called in different contexts for gigantic and
 * non-gigantic pages.
 * - For gigantic pages, this is called early in the boot process and
 *   pages are allocated from memblock allocated or something similar.
 *   Gigantic pages are actually added to pools later with the routine
 *   gather_bootmem_prealloc.
 * - For non-gigantic pages, this is called later in the boot process after
 *   all of mm is up and functional.  Pages are allocated from buddy and
 *   then added to hugetlb pools.
 */
static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
{
        unsigned long allocated;
        static bool initialized __initdata;

        /* skip gigantic hugepages allocation if hugetlb_cma enabled */
        if (hstate_is_gigantic(h) && hugetlb_cma_size) {
                pr_warn_once("HugeTLB: hugetlb_cma is enabled, skip boot time allocation\n");
                return;
        }

        /* hugetlb_hstate_alloc_pages will be called many times, initialize huge_boot_pages once */
        if (!initialized) {
                int i = 0;

                for (i = 0; i < MAX_NUMNODES; i++)
                        INIT_LIST_HEAD(&huge_boot_pages[i]);
                initialized = true;
        }

        /* do node specific alloc */
        if (hugetlb_hstate_alloc_pages_specific_nodes(h))
                return;

        /* below will do all node balanced alloc */
        if (hstate_is_gigantic(h))
                allocated = hugetlb_gigantic_pages_alloc_boot(h);
        else
                allocated = hugetlb_pages_alloc_boot(h);

        hugetlb_hstate_alloc_pages_errcheck(allocated, h);
}

static void __init hugetlb_init_hstates(void)
{
        struct hstate *h, *h2;

        for_each_hstate(h) {
                /* oversize hugepages were init'ed in early boot */
                if (!hstate_is_gigantic(h))
                        hugetlb_hstate_alloc_pages(h);

                /*
                 * Set demote order for each hstate.  Note that
                 * h->demote_order is initially 0.
                 * - We can not demote gigantic pages if runtime freeing
                 *   is not supported, so skip this.
                 * - If CMA allocation is possible, we can not demote
                 *   HUGETLB_PAGE_ORDER or smaller size pages.
                 */
                if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                        continue;
                if (hugetlb_cma_size && h->order <= HUGETLB_PAGE_ORDER)
                        continue;
                for_each_hstate(h2) {
                        if (h2 == h)
                                continue;
                        if (h2->order < h->order &&
                            h2->order > h->demote_order)
                                h->demote_order = h2->order;
                }
        }
}

static void __init report_hugepages(void)
{
        struct hstate *h;

        for_each_hstate(h) {
                char buf[32];

                string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
                pr_info("HugeTLB: registered %s page size, pre-allocated %ld pages\n",
                        buf, h->free_huge_pages);
                pr_info("HugeTLB: %d KiB vmemmap can be freed for a %s page\n",
                        hugetlb_vmemmap_optimizable_size(h) / SZ_1K, buf);
        }
}

#ifdef CONFIG_HIGHMEM
static void try_to_free_low(struct hstate *h, unsigned long count,
                                                nodemask_t *nodes_allowed)
{
        int i;
        LIST_HEAD(page_list);

        lockdep_assert_held(&hugetlb_lock);
        if (hstate_is_gigantic(h))
                return;

        /*
         * Collect pages to be freed on a list, and free after dropping lock
         */
        for_each_node_mask(i, *nodes_allowed) {
                struct folio *folio, *next;
                struct list_head *freel = &h->hugepage_freelists[i];
                list_for_each_entry_safe(folio, next, freel, lru) {
                        if (count >= h->nr_huge_pages)
                                goto out;
                        if (folio_test_highmem(folio))
                                continue;
                        remove_hugetlb_folio(h, folio, false);
                        list_add(&folio->lru, &page_list);
                }
        }

out:
        spin_unlock_irq(&hugetlb_lock);
        update_and_free_pages_bulk(h, &page_list);
        spin_lock_irq(&hugetlb_lock);
}
#else
static inline void try_to_free_low(struct hstate *h, unsigned long count,
                                                nodemask_t *nodes_allowed)
{
}
#endif

/*
 * Increment or decrement surplus_huge_pages.  Keep node-specific counters
 * balanced by operating on them in a round-robin fashion.
 * Returns 1 if an adjustment was made.
 */
static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
                                int delta)
{
        int nr_nodes, node;

        lockdep_assert_held(&hugetlb_lock);
        VM_BUG_ON(delta != -1 && delta != 1);

        if (delta < 0) {
                for_each_node_mask_to_alloc(&h->next_nid_to_alloc, nr_nodes, node, nodes_allowed) {
                        if (h->surplus_huge_pages_node[node])
                                goto found;
                }
        } else {
                for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
                        if (h->surplus_huge_pages_node[node] <
                                        h->nr_huge_pages_node[node])
                                goto found;
                }
        }
        return 0;

found:
        h->surplus_huge_pages += delta;
        h->surplus_huge_pages_node[node] += delta;
        return 1;
}

#define persistent_huge_pages(h) (h->nr_huge_pages - h->surplus_huge_pages)
static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
                              nodemask_t *nodes_allowed)
{
        unsigned long min_count;
        unsigned long allocated;
        struct folio *folio;
        LIST_HEAD(page_list);
        NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);

        /*
         * Bit mask controlling how hard we retry per-node allocations.
         * If we can not allocate the bit mask, do not attempt to allocate
         * the requested huge pages.
         */
        if (node_alloc_noretry)
                nodes_clear(*node_alloc_noretry);
        else
                return -ENOMEM;

        /*
         * resize_lock mutex prevents concurrent adjustments to number of
         * pages in hstate via the proc/sysfs interfaces.
         */
        mutex_lock(&h->resize_lock);
        flush_free_hpage_work(h);
        spin_lock_irq(&hugetlb_lock);

        /*
         * Check for a node specific request.
         * Changing node specific huge page count may require a corresponding
         * change to the global count.  In any case, the passed node mask
         * (nodes_allowed) will restrict alloc/free to the specified node.
         */
        if (nid != NUMA_NO_NODE) {
                unsigned long old_count = count;

                count += persistent_huge_pages(h) -
                         (h->nr_huge_pages_node[nid] -
                          h->surplus_huge_pages_node[nid]);
                /*
                 * User may have specified a large count value which caused the
                 * above calculation to overflow.  In this case, they wanted
                 * to allocate as many huge pages as possible.  Set count to
                 * largest possible value to align with their intention.
                 */
                if (count < old_count)
                        count = ULONG_MAX;
        }

        /*
         * Gigantic pages runtime allocation depend on the capability for large
         * page range allocation.
         * If the system does not provide this feature, return an error when
         * the user tries to allocate gigantic pages but let the user free the
         * boottime allocated gigantic pages.
         */
        if (hstate_is_gigantic(h) && !IS_ENABLED(CONFIG_CONTIG_ALLOC)) {
                if (count > persistent_huge_pages(h)) {
                        spin_unlock_irq(&hugetlb_lock);
                        mutex_unlock(&h->resize_lock);
                        NODEMASK_FREE(node_alloc_noretry);
                        return -EINVAL;
                }
                /* Fall through to decrease pool */
        }

        /*
         * Increase the pool size
         * First take pages out of surplus state.  Then make up the
         * remaining difference by allocating fresh huge pages.
         *
         * We might race with alloc_surplus_hugetlb_folio() here and be unable
         * to convert a surplus huge page to a normal huge page. That is
         * not critical, though, it just means the overall size of the
         * pool might be one hugepage larger than it needs to be, but
         * within all the constraints specified by the sysctls.
         */
        while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
                if (!adjust_pool_surplus(h, nodes_allowed, -1))
                        break;
        }

        allocated = 0;
        while (count > (persistent_huge_pages(h) + allocated)) {
                /*
                 * If this allocation races such that we no longer need the
                 * page, free_huge_folio will handle it by freeing the page
                 * and reducing the surplus.
                 */
                spin_unlock_irq(&hugetlb_lock);

                /* yield cpu to avoid soft lockup */
                cond_resched();

                folio = alloc_pool_huge_folio(h, nodes_allowed,
                                                node_alloc_noretry,
                                                &h->next_nid_to_alloc);
                if (!folio) {
                        prep_and_add_allocated_folios(h, &page_list);
                        spin_lock_irq(&hugetlb_lock);
                        goto out;
                }

                list_add(&folio->lru, &page_list);
                allocated++;

                /* Bail for signals. Probably ctrl-c from user */
                if (signal_pending(current)) {
                        prep_and_add_allocated_folios(h, &page_list);
                        spin_lock_irq(&hugetlb_lock);
                        goto out;
                }

                spin_lock_irq(&hugetlb_lock);
        }

        /* Add allocated pages to the pool */
        if (!list_empty(&page_list)) {
                spin_unlock_irq(&hugetlb_lock);
                prep_and_add_allocated_folios(h, &page_list);
                spin_lock_irq(&hugetlb_lock);
        }

        /*
         * Decrease the pool size
         * First return free pages to the buddy allocator (being careful
         * to keep enough around to satisfy reservations).  Then place
         * pages into surplus state as needed so the pool will shrink
         * to the desired size as pages become free.
         *
         * By placing pages into the surplus state independent of the
         * overcommit value, we are allowing the surplus pool size to
         * exceed overcommit. There are few sane options here. Since
         * alloc_surplus_hugetlb_folio() is checking the global counter,
         * though, we'll note that we're not allowed to exceed surplus
         * and won't grow the pool anywhere else. Not until one of the
         * sysctls are changed, or the surplus pages go out of use.
         */
        min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
        min_count = max(count, min_count);
        try_to_free_low(h, min_count, nodes_allowed);

        /*
         * Collect pages to be removed on list without dropping lock
         */
        while (min_count < persistent_huge_pages(h)) {
                folio = remove_pool_hugetlb_folio(h, nodes_allowed, 0);
                if (!folio)
                        break;

                list_add(&folio->lru, &page_list);
        }
        /* free the pages after dropping lock */
        spin_unlock_irq(&hugetlb_lock);
        update_and_free_pages_bulk(h, &page_list);
        flush_free_hpage_work(h);
        spin_lock_irq(&hugetlb_lock);

        while (count < persistent_huge_pages(h)) {
                if (!adjust_pool_surplus(h, nodes_allowed, 1))
                        break;
        }
out:
        h->max_huge_pages = persistent_huge_pages(h);
        spin_unlock_irq(&hugetlb_lock);
        mutex_unlock(&h->resize_lock);

        NODEMASK_FREE(node_alloc_noretry);

        return 0;
}

static int demote_free_hugetlb_folio(struct hstate *h, struct folio *folio)
{
        int i, nid = folio_nid(folio);
        struct hstate *target_hstate;
        struct page *subpage;
        struct folio *inner_folio;
        int rc = 0;

        target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);

        remove_hugetlb_folio_for_demote(h, folio, false);
        spin_unlock_irq(&hugetlb_lock);

        /*
         * If vmemmap already existed for folio, the remove routine above would
         * have cleared the hugetlb folio flag.  Hence the folio is technically
         * no longer a hugetlb folio.  hugetlb_vmemmap_restore_folio can only be
         * passed hugetlb folios and will BUG otherwise.
         */
        if (folio_test_hugetlb(folio)) {
                rc = hugetlb_vmemmap_restore_folio(h, folio);
                if (rc) {
                        /* Allocation of vmemmmap failed, we can not demote folio */
                        spin_lock_irq(&hugetlb_lock);
                        folio_ref_unfreeze(folio, 1);
                        add_hugetlb_folio(h, folio, false);
                        return rc;
                }
        }

        /*
         * Use destroy_compound_hugetlb_folio_for_demote for all huge page
         * sizes as it will not ref count folios.
         */
        destroy_compound_hugetlb_folio_for_demote(folio, huge_page_order(h));

        /*
         * Taking target hstate mutex synchronizes with set_max_huge_pages.
         * Without the mutex, pages added to target hstate could be marked
         * as surplus.
         *
         * Note that we already hold h->resize_lock.  To prevent deadlock,
         * use the convention of always taking larger size hstate mutex first.
         */
        mutex_lock(&target_hstate->resize_lock);
        for (i = 0; i < pages_per_huge_page(h);
                                i += pages_per_huge_page(target_hstate)) {
                subpage = folio_page(folio, i);
                inner_folio = page_folio(subpage);
                if (hstate_is_gigantic(target_hstate))
                        prep_compound_gigantic_folio_for_demote(inner_folio,
                                                        target_hstate->order);
                else
                        prep_compound_page(subpage, target_hstate->order);
                folio_change_private(inner_folio, NULL);
                prep_new_hugetlb_folio(target_hstate, inner_folio, nid);
                free_huge_folio(inner_folio);
        }
        mutex_unlock(&target_hstate->resize_lock);

        spin_lock_irq(&hugetlb_lock);

        /*
         * Not absolutely necessary, but for consistency update max_huge_pages
         * based on pool changes for the demoted page.
         */
        h->max_huge_pages--;
        target_hstate->max_huge_pages +=
                pages_per_huge_page(h) / pages_per_huge_page(target_hstate);

        return rc;
}

static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
        __must_hold(&hugetlb_lock)
{
        int nr_nodes, node;
        struct folio *folio;

        lockdep_assert_held(&hugetlb_lock);

        /* We should never get here if no demote order */
        if (!h->demote_order) {
                pr_warn("HugeTLB: NULL demote order passed to demote_pool_huge_page.\n");
                return -EINVAL;         /* internal error */
        }

        for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
                list_for_each_entry(folio, &h->hugepage_freelists[node], lru) {
                        if (folio_test_hwpoison(folio))
                                continue;
                        return demote_free_hugetlb_folio(h, folio);
                }
        }

        /*
         * Only way to get here is if all pages on free lists are poisoned.
         * Return -EBUSY so that caller will not retry.
         */
        return -EBUSY;
}

#define HSTATE_ATTR_RO(_name) \
        static struct kobj_attribute _name##_attr = __ATTR_RO(_name)

#define HSTATE_ATTR_WO(_name) \
        static struct kobj_attribute _name##_attr = __ATTR_WO(_name)

#define HSTATE_ATTR(_name) \
        static struct kobj_attribute _name##_attr = __ATTR_RW(_name)

static struct kobject *hugepages_kobj;
static struct kobject *hstate_kobjs[HUGE_MAX_HSTATE];

static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp);

static struct hstate *kobj_to_hstate(struct kobject *kobj, int *nidp)
{
        int i;

        for (i = 0; i < HUGE_MAX_HSTATE; i++)
                if (hstate_kobjs[i] == kobj) {
                        if (nidp)
                                *nidp = NUMA_NO_NODE;
                        return &hstates[i];
                }

        return kobj_to_node_hstate(kobj, nidp);
}

static ssize_t nr_hugepages_show_common(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h;
        unsigned long nr_huge_pages;
        int nid;

        h = kobj_to_hstate(kobj, &nid);
        if (nid == NUMA_NO_NODE)
                nr_huge_pages = h->nr_huge_pages;
        else
                nr_huge_pages = h->nr_huge_pages_node[nid];

        return sysfs_emit(buf, "%lu\n", nr_huge_pages);
}

static ssize_t __nr_hugepages_store_common(bool obey_mempolicy,
                                           struct hstate *h, int nid,
                                           unsigned long count, size_t len)
{
        int err;
        nodemask_t nodes_allowed, *n_mask;

        if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
                return -EINVAL;

        if (nid == NUMA_NO_NODE) {
                /*
                 * global hstate attribute
                 */
                if (!(obey_mempolicy &&
                                init_nodemask_of_mempolicy(&nodes_allowed)))
                        n_mask = &node_states[N_MEMORY];
                else
                        n_mask = &nodes_allowed;
        } else {
                /*
                 * Node specific request.  count adjustment happens in
                 * set_max_huge_pages() after acquiring hugetlb_lock.
                 */
                init_nodemask_of_node(&nodes_allowed, nid);
                n_mask = &nodes_allowed;
        }

        err = set_max_huge_pages(h, count, nid, n_mask);

        return err ? err : len;
}

static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
                                         struct kobject *kobj, const char *buf,
                                         size_t len)
{
        struct hstate *h;
        unsigned long count;
        int nid;
        int err;

        err = kstrtoul(buf, 10, &count);
        if (err)
                return err;

        h = kobj_to_hstate(kobj, &nid);
        return __nr_hugepages_store_common(obey_mempolicy, h, nid, count, len);
}

static ssize_t nr_hugepages_show(struct kobject *kobj,
                                       struct kobj_attribute *attr, char *buf)
{
        return nr_hugepages_show_common(kobj, attr, buf);
}

static ssize_t nr_hugepages_store(struct kobject *kobj,
               struct kobj_attribute *attr, const char *buf, size_t len)
{
        return nr_hugepages_store_common(false, kobj, buf, len);
}
HSTATE_ATTR(nr_hugepages);

#ifdef CONFIG_NUMA

/*
 * hstate attribute for optionally mempolicy-based constraint on persistent
 * huge page alloc/free.
 */
static ssize_t nr_hugepages_mempolicy_show(struct kobject *kobj,
                                           struct kobj_attribute *attr,
                                           char *buf)
{
        return nr_hugepages_show_common(kobj, attr, buf);
}

static ssize_t nr_hugepages_mempolicy_store(struct kobject *kobj,
               struct kobj_attribute *attr, const char *buf, size_t len)
{
        return nr_hugepages_store_common(true, kobj, buf, len);
}
HSTATE_ATTR(nr_hugepages_mempolicy);
#endif


static ssize_t nr_overcommit_hugepages_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h = kobj_to_hstate(kobj, NULL);
        return sysfs_emit(buf, "%lu\n", h->nr_overcommit_huge_pages);
}

static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        int err;
        unsigned long input;
        struct hstate *h = kobj_to_hstate(kobj, NULL);

        if (hstate_is_gigantic(h))
                return -EINVAL;

        err = kstrtoul(buf, 10, &input);
        if (err)
                return err;

        spin_lock_irq(&hugetlb_lock);
        h->nr_overcommit_huge_pages = input;
        spin_unlock_irq(&hugetlb_lock);

        return count;
}
HSTATE_ATTR(nr_overcommit_hugepages);

static ssize_t free_hugepages_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h;
        unsigned long free_huge_pages;
        int nid;

        h = kobj_to_hstate(kobj, &nid);
        if (nid == NUMA_NO_NODE)
                free_huge_pages = h->free_huge_pages;
        else
                free_huge_pages = h->free_huge_pages_node[nid];

        return sysfs_emit(buf, "%lu\n", free_huge_pages);
}
HSTATE_ATTR_RO(free_hugepages);

static ssize_t resv_hugepages_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h = kobj_to_hstate(kobj, NULL);
        return sysfs_emit(buf, "%lu\n", h->resv_huge_pages);
}
HSTATE_ATTR_RO(resv_hugepages);

static ssize_t surplus_hugepages_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h;
        unsigned long surplus_huge_pages;
        int nid;

        h = kobj_to_hstate(kobj, &nid);
        if (nid == NUMA_NO_NODE)
                surplus_huge_pages = h->surplus_huge_pages;
        else
                surplus_huge_pages = h->surplus_huge_pages_node[nid];

        return sysfs_emit(buf, "%lu\n", surplus_huge_pages);
}
HSTATE_ATTR_RO(surplus_hugepages);

static ssize_t demote_store(struct kobject *kobj,
               struct kobj_attribute *attr, const char *buf, size_t len)
{
        unsigned long nr_demote;
        unsigned long nr_available;
        nodemask_t nodes_allowed, *n_mask;
        struct hstate *h;
        int err;
        int nid;

        err = kstrtoul(buf, 10, &nr_demote);
        if (err)
                return err;
        h = kobj_to_hstate(kobj, &nid);

        if (nid != NUMA_NO_NODE) {
                init_nodemask_of_node(&nodes_allowed, nid);
                n_mask = &nodes_allowed;
        } else {
                n_mask = &node_states[N_MEMORY];
        }

        /* Synchronize with other sysfs operations modifying huge pages */
        mutex_lock(&h->resize_lock);
        spin_lock_irq(&hugetlb_lock);

        while (nr_demote) {
                /*
                 * Check for available pages to demote each time thorough the
                 * loop as demote_pool_huge_page will drop hugetlb_lock.
                 */
                if (nid != NUMA_NO_NODE)
                        nr_available = h->free_huge_pages_node[nid];
                else
                        nr_available = h->free_huge_pages;
                nr_available -= h->resv_huge_pages;
                if (!nr_available)
                        break;

                err = demote_pool_huge_page(h, n_mask);
                if (err)
                        break;

                nr_demote--;
        }

        spin_unlock_irq(&hugetlb_lock);
        mutex_unlock(&h->resize_lock);

        if (err)
                return err;
        return len;
}
HSTATE_ATTR_WO(demote);

static ssize_t demote_size_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct hstate *h = kobj_to_hstate(kobj, NULL);
        unsigned long demote_size = (PAGE_SIZE << h->demote_order) / SZ_1K;

        return sysfs_emit(buf, "%lukB\n", demote_size);
}

static ssize_t demote_size_store(struct kobject *kobj,
                                        struct kobj_attribute *attr,
                                        const char *buf, size_t count)
{
        struct hstate *h, *demote_hstate;
        unsigned long demote_size;
        unsigned int demote_order;

        demote_size = (unsigned long)memparse(buf, NULL);

        demote_hstate = size_to_hstate(demote_size);
        if (!demote_hstate)
                return -EINVAL;
        demote_order = demote_hstate->order;
        if (demote_order < HUGETLB_PAGE_ORDER)
                return -EINVAL;

        /* demote order must be smaller than hstate order */
        h = kobj_to_hstate(kobj, NULL);
        if (demote_order >= h->order)
                return -EINVAL;

        /* resize_lock synchronizes access to demote size and writes */
        mutex_lock(&h->resize_lock);
        h->demote_order = demote_order;
        mutex_unlock(&h->resize_lock);

        return count;
}
HSTATE_ATTR(demote_size);

static struct attribute *hstate_attrs[] = {
        &nr_hugepages_attr.attr,
        &nr_overcommit_hugepages_attr.attr,
        &free_hugepages_attr.attr,
        &resv_hugepages_attr.attr,
        &surplus_hugepages_attr.attr,
#ifdef CONFIG_NUMA
        &nr_hugepages_mempolicy_attr.attr,
#endif
        NULL,
};

static const struct attribute_group hstate_attr_group = {
        .attrs = hstate_attrs,
};

static struct attribute *hstate_demote_attrs[] = {
        &demote_size_attr.attr,
        &demote_attr.attr,
        NULL,
};

static const struct attribute_group hstate_demote_attr_group = {
        .attrs = hstate_demote_attrs,
};

static int hugetlb_sysfs_add_hstate(struct hstate *h, struct kobject *parent,
                                    struct kobject **hstate_kobjs,
                                    const struct attribute_group *hstate_attr_group)
{
        int retval;
        int hi = hstate_index(h);

        hstate_kobjs[hi] = kobject_create_and_add(h->name, parent);
        if (!hstate_kobjs[hi])
                return -ENOMEM;

        retval = sysfs_create_group(hstate_kobjs[hi], hstate_attr_group);
        if (retval) {
                kobject_put(hstate_kobjs[hi]);
                hstate_kobjs[hi] = NULL;
                return retval;
        }

        if (h->demote_order) {
                retval = sysfs_create_group(hstate_kobjs[hi],
                                            &hstate_demote_attr_group);
                if (retval) {
                        pr_warn("HugeTLB unable to create demote interfaces for %s\n", h->name);
                        sysfs_remove_group(hstate_kobjs[hi], hstate_attr_group);
                        kobject_put(hstate_kobjs[hi]);
                        hstate_kobjs[hi] = NULL;
                        return retval;
                }
        }

        return 0;
}

#ifdef CONFIG_NUMA
static bool hugetlb_sysfs_initialized __ro_after_init;

/*
 * node_hstate/s - associate per node hstate attributes, via their kobjects,
 * with node devices in node_devices[] using a parallel array.  The array
 * index of a node device or _hstate == node id.
 * This is here to avoid any static dependency of the node device driver, in
 * the base kernel, on the hugetlb module.
 */
struct node_hstate {
        struct kobject          *hugepages_kobj;
        struct kobject          *hstate_kobjs[HUGE_MAX_HSTATE];
};
static struct node_hstate node_hstates[MAX_NUMNODES];

/*
 * A subset of global hstate attributes for node devices
 */
static struct attribute *per_node_hstate_attrs[] = {
        &nr_hugepages_attr.attr,
        &free_hugepages_attr.attr,
        &surplus_hugepages_attr.attr,
        NULL,
};

static const struct attribute_group per_node_hstate_attr_group = {
        .attrs = per_node_hstate_attrs,
};

/*
 * kobj_to_node_hstate - lookup global hstate for node device hstate attr kobj.
 * Returns node id via non-NULL nidp.
 */
static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
{
        int nid;

        for (nid = 0; nid < nr_node_ids; nid++) {
                struct node_hstate *nhs = &node_hstates[nid];
                int i;
                for (i = 0; i < HUGE_MAX_HSTATE; i++)
                        if (nhs->hstate_kobjs[i] == kobj) {
                                if (nidp)
                                        *nidp = nid;
                                return &hstates[i];
                        }
        }

        BUG();
        return NULL;
}

/*
 * Unregister hstate attributes from a single node device.
 * No-op if no hstate attributes attached.
 */
void hugetlb_unregister_node(struct node *node)
{
        struct hstate *h;
        struct node_hstate *nhs = &node_hstates[node->dev.id];

        if (!nhs->hugepages_kobj)
                return;         /* no hstate attributes */

        for_each_hstate(h) {
                int idx = hstate_index(h);
                struct kobject *hstate_kobj = nhs->hstate_kobjs[idx];

                if (!hstate_kobj)
                        continue;
                if (h->demote_order)
                        sysfs_remove_group(hstate_kobj, &hstate_demote_attr_group);
                sysfs_remove_group(hstate_kobj, &per_node_hstate_attr_group);
                kobject_put(hstate_kobj);
                nhs->hstate_kobjs[idx] = NULL;
        }

        kobject_put(nhs->hugepages_kobj);
        nhs->hugepages_kobj = NULL;
}


/*
 * Register hstate attributes for a single node device.
 * No-op if attributes already registered.
 */
void hugetlb_register_node(struct node *node)
{
        struct hstate *h;
        struct node_hstate *nhs = &node_hstates[node->dev.id];
        int err;

        if (!hugetlb_sysfs_initialized)
                return;

        if (nhs->hugepages_kobj)
                return;         /* already allocated */

        nhs->hugepages_kobj = kobject_create_and_add("hugepages",
                                                        &node->dev.kobj);
        if (!nhs->hugepages_kobj)
                return;

        for_each_hstate(h) {
                err = hugetlb_sysfs_add_hstate(h, nhs->hugepages_kobj,
                                                nhs->hstate_kobjs,
                                                &per_node_hstate_attr_group);
                if (err) {
                        pr_err("HugeTLB: Unable to add hstate %s for node %d\n",
                                h->name, node->dev.id);
                        hugetlb_unregister_node(node);
                        break;
                }
        }
}

/*
 * hugetlb init time:  register hstate attributes for all registered node
 * devices of nodes that have memory.  All on-line nodes should have
 * registered their associated device by this time.
 */
static void __init hugetlb_register_all_nodes(void)
{
        int nid;

        for_each_online_node(nid)
                hugetlb_register_node(node_devices[nid]);
}
#else   /* !CONFIG_NUMA */

static struct hstate *kobj_to_node_hstate(struct kobject *kobj, int *nidp)
{
        BUG();
        if (nidp)
                *nidp = -1;
        return NULL;
}

static void hugetlb_register_all_nodes(void) { }

#endif

#ifdef CONFIG_CMA
static void __init hugetlb_cma_check(void);
#else
static inline __init void hugetlb_cma_check(void)
{
}
#endif

static void __init hugetlb_sysfs_init(void)
{
        struct hstate *h;
        int err;

        hugepages_kobj = kobject_create_and_add("hugepages", mm_kobj);
        if (!hugepages_kobj)
                return;

        for_each_hstate(h) {
                err = hugetlb_sysfs_add_hstate(h, hugepages_kobj,
                                         hstate_kobjs, &hstate_attr_group);
                if (err)
                        pr_err("HugeTLB: Unable to add hstate %s", h->name);
        }

#ifdef CONFIG_NUMA
        hugetlb_sysfs_initialized = true;
#endif
        hugetlb_register_all_nodes();
}

#ifdef CONFIG_SYSCTL
static void hugetlb_sysctl_init(void);
#else
static inline void hugetlb_sysctl_init(void) { }
#endif

static int __init hugetlb_init(void)
{
        int i;

        BUILD_BUG_ON(sizeof_field(struct page, private) * BITS_PER_BYTE <
                        __NR_HPAGEFLAGS);

        if (!hugepages_supported()) {
                if (hugetlb_max_hstate || default_hstate_max_huge_pages)
                        pr_warn("HugeTLB: huge pages not supported, ignoring associated command-line parameters\n");
                return 0;
        }

        /*
         * Make sure HPAGE_SIZE (HUGETLB_PAGE_ORDER) hstate exists.  Some
         * architectures depend on setup being done here.
         */
        hugetlb_add_hstate(HUGETLB_PAGE_ORDER);
        if (!parsed_default_hugepagesz) {
                /*
                 * If we did not parse a default huge page size, set
                 * default_hstate_idx to HPAGE_SIZE hstate. And, if the
                 * number of huge pages for this default size was implicitly
                 * specified, set that here as well.
                 * Note that the implicit setting will overwrite an explicit
                 * setting.  A warning will be printed in this case.
                 */
                default_hstate_idx = hstate_index(size_to_hstate(HPAGE_SIZE));
                if (default_hstate_max_huge_pages) {
                        if (default_hstate.max_huge_pages) {
                                char buf[32];

                                string_get_size(huge_page_size(&default_hstate),
                                        1, STRING_UNITS_2, buf, 32);
                                pr_warn("HugeTLB: Ignoring hugepages=%lu associated with %s page size\n",
                                        default_hstate.max_huge_pages, buf);
                                pr_warn("HugeTLB: Using hugepages=%lu for number of default huge pages\n",
                                        default_hstate_max_huge_pages);
                        }
                        default_hstate.max_huge_pages =
                                default_hstate_max_huge_pages;

                        for_each_online_node(i)
                                default_hstate.max_huge_pages_node[i] =
                                        default_hugepages_in_node[i];
                }
        }

        hugetlb_cma_check();
        hugetlb_init_hstates();
        gather_bootmem_prealloc();
        report_hugepages();

        hugetlb_sysfs_init();
        hugetlb_cgroup_file_init();
        hugetlb_sysctl_init();

#ifdef CONFIG_SMP
        num_fault_mutexes = roundup_pow_of_two(8 * num_possible_cpus());
#else
        num_fault_mutexes = 1;
#endif
        hugetlb_fault_mutex_table =
                kmalloc_array(num_fault_mutexes, sizeof(struct mutex),
                              GFP_KERNEL);
        BUG_ON(!hugetlb_fault_mutex_table);

        for (i = 0; i < num_fault_mutexes; i++)
                mutex_init(&hugetlb_fault_mutex_table[i]);
        return 0;
}
subsys_initcall(hugetlb_init);

/* Overwritten by architectures with more huge page sizes */
bool __init __attribute((weak)) arch_hugetlb_valid_size(unsigned long size)
{
        return size == HPAGE_SIZE;
}

void __init hugetlb_add_hstate(unsigned int order)
{
        struct hstate *h;
        unsigned long i;

        if (size_to_hstate(PAGE_SIZE << order)) {
                return;
        }
        BUG_ON(hugetlb_max_hstate >= HUGE_MAX_HSTATE);
        BUG_ON(order < order_base_2(__NR_USED_SUBPAGE));
        h = &hstates[hugetlb_max_hstate++];
        mutex_init(&h->resize_lock);
        h->order = order;
        h->mask = ~(huge_page_size(h) - 1);
        for (i = 0; i < MAX_NUMNODES; ++i)
                INIT_LIST_HEAD(&h->hugepage_freelists[i]);
        INIT_LIST_HEAD(&h->hugepage_activelist);
        h->next_nid_to_alloc = first_memory_node;
        h->next_nid_to_free = first_memory_node;
        snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
                                        huge_page_size(h)/SZ_1K);

        parsed_hstate = h;
}

bool __init __weak hugetlb_node_alloc_supported(void)
{
        return true;
}

static void __init hugepages_clear_pages_in_node(void)
{
        if (!hugetlb_max_hstate) {
                default_hstate_max_huge_pages = 0;
                memset(default_hugepages_in_node, 0,
                        sizeof(default_hugepages_in_node));
        } else {
                parsed_hstate->max_huge_pages = 0;
                memset(parsed_hstate->max_huge_pages_node, 0,
                        sizeof(parsed_hstate->max_huge_pages_node));
        }
}

/*
 * hugepages command line processing
 * hugepages normally follows a valid hugepagsz or default_hugepagsz
 * specification.  If not, ignore the hugepages value.  hugepages can also
 * be the first huge page command line  option in which case it implicitly
 * specifies the number of huge pages for the default size.
 */
static int __init hugepages_setup(char *s)
{
        unsigned long *mhp;
        static unsigned long *last_mhp;
        int node = NUMA_NO_NODE;
        int count;
        unsigned long tmp;
        char *p = s;

        if (!parsed_valid_hugepagesz) {
                pr_warn("HugeTLB: hugepages=%s does not follow a valid hugepagesz, ignoring\n", s);
                parsed_valid_hugepagesz = true;
                return 1;
        }

        /*
         * !hugetlb_max_hstate means we haven't parsed a hugepagesz= parameter
         * yet, so this hugepages= parameter goes to the "default hstate".
         * Otherwise, it goes with the previously parsed hugepagesz or
         * default_hugepagesz.
         */
        else if (!hugetlb_max_hstate)
                mhp = &default_hstate_max_huge_pages;
        else
                mhp = &parsed_hstate->max_huge_pages;

        if (mhp == last_mhp) {
                pr_warn("HugeTLB: hugepages= specified twice without interleaving hugepagesz=, ignoring hugepages=%s\n", s);
                return 1;
        }

        while (*p) {
                count = 0;
                if (sscanf(p, "%lu%n", &tmp, &count) != 1)
                        goto invalid;
                /* Parameter is node format */
                if (p[count] == ':') {
                        if (!hugetlb_node_alloc_supported()) {
                                pr_warn("HugeTLB: architecture can't support node specific alloc, ignoring!\n");
                                return 1;
                        }
                        if (tmp >= MAX_NUMNODES || !node_online(tmp))
                                goto invalid;
                        node = array_index_nospec(tmp, MAX_NUMNODES);
                        p += count + 1;
                        /* Parse hugepages */
                        if (sscanf(p, "%lu%n", &tmp, &count) != 1)
                                goto invalid;
                        if (!hugetlb_max_hstate)
                                default_hugepages_in_node[node] = tmp;
                        else
                                parsed_hstate->max_huge_pages_node[node] = tmp;
                        *mhp += tmp;
                        /* Go to parse next node*/
                        if (p[count] == ',')
                                p += count + 1;
                        else
                                break;
                } else {
                        if (p != s)
                                goto invalid;
                        *mhp = tmp;
                        break;
                }
        }

        /*
         * Global state is always initialized later in hugetlb_init.
         * But we need to allocate gigantic hstates here early to still
         * use the bootmem allocator.
         */
        if (hugetlb_max_hstate && hstate_is_gigantic(parsed_hstate))
                hugetlb_hstate_alloc_pages(parsed_hstate);

        last_mhp = mhp;

        return 1;

invalid:
        pr_warn("HugeTLB: Invalid hugepages parameter %s\n", p);
        hugepages_clear_pages_in_node();
        return 1;
}
__setup("hugepages=", hugepages_setup);

/*
 * hugepagesz command line processing
 * A specific huge page size can only be specified once with hugepagesz.
 * hugepagesz is followed by hugepages on the command line.  The global
 * variable 'parsed_valid_hugepagesz' is used to determine if prior
 * hugepagesz argument was valid.
 */
static int __init hugepagesz_setup(char *s)
{
        unsigned long size;
        struct hstate *h;

        parsed_valid_hugepagesz = false;
        size = (unsigned long)memparse(s, NULL);

        if (!arch_hugetlb_valid_size(size)) {
                pr_err("HugeTLB: unsupported hugepagesz=%s\n", s);
                return 1;
        }

        h = size_to_hstate(size);
        if (h) {
                /*
                 * hstate for this size already exists.  This is normally
                 * an error, but is allowed if the existing hstate is the
                 * default hstate.  More specifically, it is only allowed if
                 * the number of huge pages for the default hstate was not
                 * previously specified.
                 */
                if (!parsed_default_hugepagesz ||  h != &default_hstate ||
                    default_hstate.max_huge_pages) {
                        pr_warn("HugeTLB: hugepagesz=%s specified twice, ignoring\n", s);
                        return 1;
                }

                /*
                 * No need to call hugetlb_add_hstate() as hstate already
                 * exists.  But, do set parsed_hstate so that a following
                 * hugepages= parameter will be applied to this hstate.
                 */
                parsed_hstate = h;
                parsed_valid_hugepagesz = true;
                return 1;
        }

        hugetlb_add_hstate(ilog2(size) - PAGE_SHIFT);
        parsed_valid_hugepagesz = true;
        return 1;
}
__setup("hugepagesz=", hugepagesz_setup);

/*
 * default_hugepagesz command line input
 * Only one instance of default_hugepagesz allowed on command line.
 */
static int __init default_hugepagesz_setup(char *s)
{
        unsigned long size;
        int i;

        parsed_valid_hugepagesz = false;
        if (parsed_default_hugepagesz) {
                pr_err("HugeTLB: default_hugepagesz previously specified, ignoring %s\n", s);
                return 1;
        }

        size = (unsigned long)memparse(s, NULL);

        if (!arch_hugetlb_valid_size(size)) {
                pr_err("HugeTLB: unsupported default_hugepagesz=%s\n", s);
                return 1;
        }

        hugetlb_add_hstate(ilog2(size) - PAGE_SHIFT);
        parsed_valid_hugepagesz = true;
        parsed_default_hugepagesz = true;
        default_hstate_idx = hstate_index(size_to_hstate(size));

        /*
         * The number of default huge pages (for this size) could have been
         * specified as the first hugetlb parameter: hugepages=X.  If so,
         * then default_hstate_max_huge_pages is set.  If the default huge
         * page size is gigantic (> MAX_PAGE_ORDER), then the pages must be
         * allocated here from bootmem allocator.
         */
        if (default_hstate_max_huge_pages) {
                default_hstate.max_huge_pages = default_hstate_max_huge_pages;
                for_each_online_node(i)
                        default_hstate.max_huge_pages_node[i] =
                                default_hugepages_in_node[i];
                if (hstate_is_gigantic(&default_hstate))
                        hugetlb_hstate_alloc_pages(&default_hstate);
                default_hstate_max_huge_pages = 0;
        }

        return 1;
}
__setup("default_hugepagesz=", default_hugepagesz_setup);

static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
{
#ifdef CONFIG_NUMA
        struct mempolicy *mpol = get_task_policy(current);

        /*
         * Only enforce MPOL_BIND policy which overlaps with cpuset policy
         * (from policy_nodemask) specifically for hugetlb case
         */
        if (mpol->mode == MPOL_BIND &&
                (apply_policy_zone(mpol, gfp_zone(gfp)) &&
                 cpuset_nodemask_valid_mems_allowed(&mpol->nodes)))
                return &mpol->nodes;
#endif
        return NULL;
}

static unsigned int allowed_mems_nr(struct hstate *h)
{
        int node;
        unsigned int nr = 0;
        nodemask_t *mbind_nodemask;
        unsigned int *array = h->free_huge_pages_node;
        gfp_t gfp_mask = htlb_alloc_mask(h);

        mbind_nodemask = policy_mbind_nodemask(gfp_mask);
        for_each_node_mask(node, cpuset_current_mems_allowed) {
                if (!mbind_nodemask || node_isset(node, *mbind_nodemask))
                        nr += array[node];
        }

        return nr;
}

#ifdef CONFIG_SYSCTL
static int proc_hugetlb_doulongvec_minmax(struct ctl_table *table, int write,
                                          void *buffer, size_t *length,
                                          loff_t *ppos, unsigned long *out)
{
        struct ctl_table dup_table;

        /*
         * In order to avoid races with __do_proc_doulongvec_minmax(), we
         * can duplicate the @table and alter the duplicate of it.
         */
        dup_table = *table;
        dup_table.data = out;

        return proc_doulongvec_minmax(&dup_table, write, buffer, length, ppos);
}

static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
                         struct ctl_table *table, int write,
                         void *buffer, size_t *length, loff_t *ppos)
{
        struct hstate *h = &default_hstate;
        unsigned long tmp = h->max_huge_pages;
        int ret;

        if (!hugepages_supported())
                return -EOPNOTSUPP;

        ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos,
                                             &tmp);
        if (ret)
                goto out;

        if (write)
                ret = __nr_hugepages_store_common(obey_mempolicy, h,
                                                  NUMA_NO_NODE, tmp, *length);
out:
        return ret;
}

static int hugetlb_sysctl_handler(struct ctl_table *table, int write,
                          void *buffer, size_t *length, loff_t *ppos)
{

        return hugetlb_sysctl_handler_common(false, table, write,
                                                        buffer, length, ppos);
}

#ifdef CONFIG_NUMA
static int hugetlb_mempolicy_sysctl_handler(struct ctl_table *table, int write,
                          void *buffer, size_t *length, loff_t *ppos)
{
        return hugetlb_sysctl_handler_common(true, table, write,
                                                        buffer, length, ppos);
}
#endif /* CONFIG_NUMA */

static int hugetlb_overcommit_handler(struct ctl_table *table, int write,
                void *buffer, size_t *length, loff_t *ppos)
{
        struct hstate *h = &default_hstate;
        unsigned long tmp;
        int ret;

        if (!hugepages_supported())
                return -EOPNOTSUPP;

        tmp = h->nr_overcommit_huge_pages;

        if (write && hstate_is_gigantic(h))
                return -EINVAL;

        ret = proc_hugetlb_doulongvec_minmax(table, write, buffer, length, ppos,
                                             &tmp);
        if (ret)
                goto out;

        if (write) {
                spin_lock_irq(&hugetlb_lock);
                h->nr_overcommit_huge_pages = tmp;
                spin_unlock_irq(&hugetlb_lock);
        }
out:
        return ret;
}

static struct ctl_table hugetlb_table[] = {
        {
                .procname       = "nr_hugepages",
                .data           = NULL,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = hugetlb_sysctl_handler,
        },
#ifdef CONFIG_NUMA
        {
                .procname       = "nr_hugepages_mempolicy",
                .data           = NULL,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = &hugetlb_mempolicy_sysctl_handler,
        },
#endif
        {
                .procname       = "hugetlb_shm_group",
                .data           = &sysctl_hugetlb_shm_group,
                .maxlen         = sizeof(gid_t),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
        {
                .procname       = "nr_overcommit_hugepages",
                .data           = NULL,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = hugetlb_overcommit_handler,
        },
};

static void hugetlb_sysctl_init(void)
{
        register_sysctl_init("vm", hugetlb_table);
}
#endif /* CONFIG_SYSCTL */

void hugetlb_report_meminfo(struct seq_file *m)
{
        struct hstate *h;
        unsigned long total = 0;

        if (!hugepages_supported())
                return;

        for_each_hstate(h) {
                unsigned long count = h->nr_huge_pages;

                total += huge_page_size(h) * count;

                if (h == &default_hstate)
                        seq_printf(m,
                                   "HugePages_Total:   %5lu\n"
                                   "HugePages_Free:    %5lu\n"
                                   "HugePages_Rsvd:    %5lu\n"
                                   "HugePages_Surp:    %5lu\n"
                                   "Hugepagesize:   %8lu kB\n",
                                   count,
                                   h->free_huge_pages,
                                   h->resv_huge_pages,
                                   h->surplus_huge_pages,
                                   huge_page_size(h) / SZ_1K);
        }

        seq_printf(m, "Hugetlb:        %8lu kB\n", total / SZ_1K);
}

int hugetlb_report_node_meminfo(char *buf, int len, int nid)
{
        struct hstate *h = &default_hstate;

        if (!hugepages_supported())
                return 0;

        return sysfs_emit_at(buf, len,
                             "Node %d HugePages_Total: %5u\n"
                             "Node %d HugePages_Free:  %5u\n"
                             "Node %d HugePages_Surp:  %5u\n",
                             nid, h->nr_huge_pages_node[nid],
                             nid, h->free_huge_pages_node[nid],
                             nid, h->surplus_huge_pages_node[nid]);
}

void hugetlb_show_meminfo_node(int nid)
{
        struct hstate *h;

        if (!hugepages_supported())
                return;

        for_each_hstate(h)
                printk("Node %d hugepages_total=%u hugepages_free=%u hugepages_surp=%u hugepages_size=%lukB\n",
                        nid,
                        h->nr_huge_pages_node[nid],
                        h->free_huge_pages_node[nid],
                        h->surplus_huge_pages_node[nid],
                        huge_page_size(h) / SZ_1K);
}

void hugetlb_report_usage(struct seq_file *m, struct mm_struct *mm)
{
        seq_printf(m, "HugetlbPages:\t%8lu kB\n",
                   K(atomic_long_read(&mm->hugetlb_usage)));
}

/* Return the number pages of memory we physically have, in PAGE_SIZE units. */
unsigned long hugetlb_total_pages(void)
{
        struct hstate *h;
        unsigned long nr_total_pages = 0;

        for_each_hstate(h)
                nr_total_pages += h->nr_huge_pages * pages_per_huge_page(h);
        return nr_total_pages;
}

static int hugetlb_acct_memory(struct hstate *h, long delta)
{
        int ret = -ENOMEM;

        if (!delta)
                return 0;

        spin_lock_irq(&hugetlb_lock);
        /*
         * When cpuset is configured, it breaks the strict hugetlb page
         * reservation as the accounting is done on a global variable. Such
         * reservation is completely rubbish in the presence of cpuset because
         * the reservation is not checked against page availability for the
         * current cpuset. Application can still potentially OOM'ed by kernel
         * with lack of free htlb page in cpuset that the task is in.
         * Attempt to enforce strict accounting with cpuset is almost
         * impossible (or too ugly) because cpuset is too fluid that
         * task or memory node can be dynamically moved between cpusets.
         *
         * The change of semantics for shared hugetlb mapping with cpuset is
         * undesirable. However, in order to preserve some of the semantics,
         * we fall back to check against current free page availability as
         * a best attempt and hopefully to minimize the impact of changing
         * semantics that cpuset has.
         *
         * Apart from cpuset, we also have memory policy mechanism that
         * also determines from which node the kernel will allocate memory
         * in a NUMA system. So similar to cpuset, we also should consider
         * the memory policy of the current task. Similar to the description
         * above.
         */
        if (delta > 0) {
                if (gather_surplus_pages(h, delta) < 0)
                        goto out;

                if (delta > allowed_mems_nr(h)) {
                        return_unused_surplus_pages(h, delta);
                        goto out;
                }
        }

        ret = 0;
        if (delta < 0)
                return_unused_surplus_pages(h, (unsigned long) -delta);

out:
        spin_unlock_irq(&hugetlb_lock);
        return ret;
}

static void hugetlb_vm_op_open(struct vm_area_struct *vma)
{
        struct resv_map *resv = vma_resv_map(vma);

        /*
         * HPAGE_RESV_OWNER indicates a private mapping.
         * This new VMA should share its siblings reservation map if present.
         * The VMA will only ever have a valid reservation map pointer where
         * it is being copied for another still existing VMA.  As that VMA
         * has a reference to the reservation map it cannot disappear until
         * after this open call completes.  It is therefore safe to take a
         * new reference here without additional locking.
         */
        if (resv && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                resv_map_dup_hugetlb_cgroup_uncharge_info(resv);
                kref_get(&resv->refs);
        }

        /*
         * vma_lock structure for sharable mappings is vma specific.
         * Clear old pointer (if copied via vm_area_dup) and allocate
         * new structure.  Before clearing, make sure vma_lock is not
         * for this vma.
         */
        if (vma->vm_flags & VM_MAYSHARE) {
                struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;

                if (vma_lock) {
                        if (vma_lock->vma != vma) {
                                vma->vm_private_data = NULL;
                                hugetlb_vma_lock_alloc(vma);
                        } else
                                pr_warn("HugeTLB: vma_lock already exists in %s.\n", __func__);
                } else
                        hugetlb_vma_lock_alloc(vma);
        }
}

static void hugetlb_vm_op_close(struct vm_area_struct *vma)
{
        struct hstate *h = hstate_vma(vma);
        struct resv_map *resv;
        struct hugepage_subpool *spool = subpool_vma(vma);
        unsigned long reserve, start, end;
        long gbl_reserve;

        hugetlb_vma_lock_free(vma);

        resv = vma_resv_map(vma);
        if (!resv || !is_vma_resv_set(vma, HPAGE_RESV_OWNER))
                return;

        start = vma_hugecache_offset(h, vma, vma->vm_start);
        end = vma_hugecache_offset(h, vma, vma->vm_end);

        reserve = (end - start) - region_count(resv, start, end);
        hugetlb_cgroup_uncharge_counter(resv, start, end);
        if (reserve) {
                /*
                 * Decrement reserve counts.  The global reserve count may be
                 * adjusted if the subpool has a minimum size.
                 */
                gbl_reserve = hugepage_subpool_put_pages(spool, reserve);
                hugetlb_acct_memory(h, -gbl_reserve);
        }

        kref_put(&resv->refs, resv_map_release);
}

static int hugetlb_vm_op_split(struct vm_area_struct *vma, unsigned long addr)
{
        if (addr & ~(huge_page_mask(hstate_vma(vma))))
                return -EINVAL;

        /*
         * PMD sharing is only possible for PUD_SIZE-aligned address ranges
         * in HugeTLB VMAs. If we will lose PUD_SIZE alignment due to this
         * split, unshare PMDs in the PUD_SIZE interval surrounding addr now.
         */
        if (addr & ~PUD_MASK) {
                /*
                 * hugetlb_vm_op_split is called right before we attempt to
                 * split the VMA. We will need to unshare PMDs in the old and
                 * new VMAs, so let's unshare before we split.
                 */
                unsigned long floor = addr & PUD_MASK;
                unsigned long ceil = floor + PUD_SIZE;

                if (floor >= vma->vm_start && ceil <= vma->vm_end)
                        hugetlb_unshare_pmds(vma, floor, ceil);
        }

        return 0;
}

static unsigned long hugetlb_vm_op_pagesize(struct vm_area_struct *vma)
{
        return huge_page_size(hstate_vma(vma));
}

/*
 * We cannot handle pagefaults against hugetlb pages at all.  They cause
 * handle_mm_fault() to try to instantiate regular-sized pages in the
 * hugepage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
 * this far.
 */
static vm_fault_t hugetlb_vm_op_fault(struct vm_fault *vmf)
{
        BUG();
        return 0;
}

/*
 * When a new function is introduced to vm_operations_struct and added
 * to hugetlb_vm_ops, please consider adding the function to shm_vm_ops.
 * This is because under System V memory model, mappings created via
 * shmget/shmat with "huge page" specified are backed by hugetlbfs files,
 * their original vm_ops are overwritten with shm_vm_ops.
 */
const struct vm_operations_struct hugetlb_vm_ops = {
        .fault = hugetlb_vm_op_fault,
        .open = hugetlb_vm_op_open,
        .close = hugetlb_vm_op_close,
        .may_split = hugetlb_vm_op_split,
        .pagesize = hugetlb_vm_op_pagesize,
};

static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
                                int writable)
{
        pte_t entry;
        unsigned int shift = huge_page_shift(hstate_vma(vma));

        if (writable) {
                entry = huge_pte_mkwrite(huge_pte_mkdirty(mk_huge_pte(page,
                                         vma->vm_page_prot)));
        } else {
                entry = huge_pte_wrprotect(mk_huge_pte(page,
                                           vma->vm_page_prot));
        }
        entry = pte_mkyoung(entry);
        entry = arch_make_huge_pte(entry, shift, vma->vm_flags);

        return entry;
}

static void set_huge_ptep_writable(struct vm_area_struct *vma,
                                   unsigned long address, pte_t *ptep)
{
        pte_t entry;

        entry = huge_pte_mkwrite(huge_pte_mkdirty(huge_ptep_get(ptep)));
        if (huge_ptep_set_access_flags(vma, address, ptep, entry, 1))
                update_mmu_cache(vma, address, ptep);
}

bool is_hugetlb_entry_migration(pte_t pte)
{
        swp_entry_t swp;

        if (huge_pte_none(pte) || pte_present(pte))
                return false;
        swp = pte_to_swp_entry(pte);
        if (is_migration_entry(swp))
                return true;
        else
                return false;
}

bool is_hugetlb_entry_hwpoisoned(pte_t pte)
{
        swp_entry_t swp;

        if (huge_pte_none(pte) || pte_present(pte))
                return false;
        swp = pte_to_swp_entry(pte);
        if (is_hwpoison_entry(swp))
                return true;
        else
                return false;
}

static void
hugetlb_install_folio(struct vm_area_struct *vma, pte_t *ptep, unsigned long addr,
                      struct folio *new_folio, pte_t old, unsigned long sz)
{
        pte_t newpte = make_huge_pte(vma, &new_folio->page, 1);

        __folio_mark_uptodate(new_folio);
        hugetlb_add_new_anon_rmap(new_folio, vma, addr);
        if (userfaultfd_wp(vma) && huge_pte_uffd_wp(old))
                newpte = huge_pte_mkuffd_wp(newpte);
        set_huge_pte_at(vma->vm_mm, addr, ptep, newpte, sz);
        hugetlb_count_add(pages_per_huge_page(hstate_vma(vma)), vma->vm_mm);
        folio_set_hugetlb_migratable(new_folio);
}

int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
                            struct vm_area_struct *dst_vma,
                            struct vm_area_struct *src_vma)
{
        pte_t *src_pte, *dst_pte, entry;
        struct folio *pte_folio;
        unsigned long addr;
        bool cow = is_cow_mapping(src_vma->vm_flags);
        struct hstate *h = hstate_vma(src_vma);
        unsigned long sz = huge_page_size(h);
        unsigned long npages = pages_per_huge_page(h);
        struct mmu_notifier_range range;
        unsigned long last_addr_mask;
        int ret = 0;

        if (cow) {
                mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, src,
                                        src_vma->vm_start,
                                        src_vma->vm_end);
                mmu_notifier_invalidate_range_start(&range);
                vma_assert_write_locked(src_vma);
                raw_write_seqcount_begin(&src->write_protect_seq);
        } else {
                /*
                 * For shared mappings the vma lock must be held before
                 * calling hugetlb_walk() in the src vma. Otherwise, the
                 * returned ptep could go away if part of a shared pmd and
                 * another thread calls huge_pmd_unshare.
                 */
                hugetlb_vma_lock_read(src_vma);
        }

        last_addr_mask = hugetlb_mask_last_page(h);
        for (addr = src_vma->vm_start; addr < src_vma->vm_end; addr += sz) {
                spinlock_t *src_ptl, *dst_ptl;
                src_pte = hugetlb_walk(src_vma, addr, sz);
                if (!src_pte) {
                        addr |= last_addr_mask;
                        continue;
                }
                dst_pte = huge_pte_alloc(dst, dst_vma, addr, sz);
                if (!dst_pte) {
                        ret = -ENOMEM;
                        break;
                }

                /*
                 * If the pagetables are shared don't copy or take references.
                 *
                 * dst_pte == src_pte is the common case of src/dest sharing.
                 * However, src could have 'unshared' and dst shares with
                 * another vma. So page_count of ptep page is checked instead
                 * to reliably determine whether pte is shared.
                 */
                if (page_count(virt_to_page(dst_pte)) > 1) {
                        addr |= last_addr_mask;
                        continue;
                }

                dst_ptl = huge_pte_lock(h, dst, dst_pte);
                src_ptl = huge_pte_lockptr(h, src, src_pte);
                spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
                entry = huge_ptep_get(src_pte);
again:
                if (huge_pte_none(entry)) {
                        /*
                         * Skip if src entry none.
                         */
                        ;
                } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) {
                        if (!userfaultfd_wp(dst_vma))
                                entry = huge_pte_clear_uffd_wp(entry);
                        set_huge_pte_at(dst, addr, dst_pte, entry, sz);
                } else if (unlikely(is_hugetlb_entry_migration(entry))) {
                        swp_entry_t swp_entry = pte_to_swp_entry(entry);
                        bool uffd_wp = pte_swp_uffd_wp(entry);

                        if (!is_readable_migration_entry(swp_entry) && cow) {
                                /*
                                 * COW mappings require pages in both
                                 * parent and child to be set to read.
                                 */
                                swp_entry = make_readable_migration_entry(
                                                        swp_offset(swp_entry));
                                entry = swp_entry_to_pte(swp_entry);
                                if (userfaultfd_wp(src_vma) && uffd_wp)
                                        entry = pte_swp_mkuffd_wp(entry);
                                set_huge_pte_at(src, addr, src_pte, entry, sz);
                        }
                        if (!userfaultfd_wp(dst_vma))
                                entry = huge_pte_clear_uffd_wp(entry);
                        set_huge_pte_at(dst, addr, dst_pte, entry, sz);
                } else if (unlikely(is_pte_marker(entry))) {
                        pte_marker marker = copy_pte_marker(
                                pte_to_swp_entry(entry), dst_vma);

                        if (marker)
                                set_huge_pte_at(dst, addr, dst_pte,
                                                make_pte_marker(marker), sz);
                } else {
                        entry = huge_ptep_get(src_pte);
                        pte_folio = page_folio(pte_page(entry));
                        folio_get(pte_folio);

                        /*
                         * Failing to duplicate the anon rmap is a rare case
                         * where we see pinned hugetlb pages while they're
                         * prone to COW. We need to do the COW earlier during
                         * fork.
                         *
                         * When pre-allocating the page or copying data, we
                         * need to be without the pgtable locks since we could
                         * sleep during the process.
                         */
                        if (!folio_test_anon(pte_folio)) {
                                hugetlb_add_file_rmap(pte_folio);
                        } else if (hugetlb_try_dup_anon_rmap(pte_folio, src_vma)) {
                                pte_t src_pte_old = entry;
                                struct folio *new_folio;

                                spin_unlock(src_ptl);
                                spin_unlock(dst_ptl);
                                /* Do not use reserve as it's private owned */
                                new_folio = alloc_hugetlb_folio(dst_vma, addr, 1);
                                if (IS_ERR(new_folio)) {
                                        folio_put(pte_folio);
                                        ret = PTR_ERR(new_folio);
                                        break;
                                }
                                ret = copy_user_large_folio(new_folio,
                                                            pte_folio,
                                                            addr, dst_vma);
                                folio_put(pte_folio);
                                if (ret) {
                                        folio_put(new_folio);
                                        break;
                                }

                                /* Install the new hugetlb folio if src pte stable */
                                dst_ptl = huge_pte_lock(h, dst, dst_pte);
                                src_ptl = huge_pte_lockptr(h, src, src_pte);
                                spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
                                entry = huge_ptep_get(src_pte);
                                if (!pte_same(src_pte_old, entry)) {
                                        restore_reserve_on_error(h, dst_vma, addr,
                                                                new_folio);
                                        folio_put(new_folio);
                                        /* huge_ptep of dst_pte won't change as in child */
                                        goto again;
                                }
                                hugetlb_install_folio(dst_vma, dst_pte, addr,
                                                      new_folio, src_pte_old, sz);
                                spin_unlock(src_ptl);
                                spin_unlock(dst_ptl);
                                continue;
                        }

                        if (cow) {
                                /*
                                 * No need to notify as we are downgrading page
                                 * table protection not changing it to point
                                 * to a new page.
                                 *
                                 * See Documentation/mm/mmu_notifier.rst
                                 */
                                huge_ptep_set_wrprotect(src, addr, src_pte);
                                entry = huge_pte_wrprotect(entry);
                        }

                        if (!userfaultfd_wp(dst_vma))
                                entry = huge_pte_clear_uffd_wp(entry);

                        set_huge_pte_at(dst, addr, dst_pte, entry, sz);
                        hugetlb_count_add(npages, dst);
                }
                spin_unlock(src_ptl);
                spin_unlock(dst_ptl);
        }

        if (cow) {
                raw_write_seqcount_end(&src->write_protect_seq);
                mmu_notifier_invalidate_range_end(&range);
        } else {
                hugetlb_vma_unlock_read(src_vma);
        }

        return ret;
}

static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr,
                          unsigned long new_addr, pte_t *src_pte, pte_t *dst_pte,
                          unsigned long sz)
{
        struct hstate *h = hstate_vma(vma);
        struct mm_struct *mm = vma->vm_mm;
        spinlock_t *src_ptl, *dst_ptl;
        pte_t pte;

        dst_ptl = huge_pte_lock(h, mm, dst_pte);
        src_ptl = huge_pte_lockptr(h, mm, src_pte);

        /*
         * We don't have to worry about the ordering of src and dst ptlocks
         * because exclusive mmap_lock (or the i_mmap_lock) prevents deadlock.
         */
        if (src_ptl != dst_ptl)
                spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);

        pte = huge_ptep_get_and_clear(mm, old_addr, src_pte);
        set_huge_pte_at(mm, new_addr, dst_pte, pte, sz);

        if (src_ptl != dst_ptl)
                spin_unlock(src_ptl);
        spin_unlock(dst_ptl);
}

int move_hugetlb_page_tables(struct vm_area_struct *vma,
                             struct vm_area_struct *new_vma,
                             unsigned long old_addr, unsigned long new_addr,
                             unsigned long len)
{
        struct hstate *h = hstate_vma(vma);
        struct address_space *mapping = vma->vm_file->f_mapping;
        unsigned long sz = huge_page_size(h);
        struct mm_struct *mm = vma->vm_mm;
        unsigned long old_end = old_addr + len;
        unsigned long last_addr_mask;
        pte_t *src_pte, *dst_pte;
        struct mmu_notifier_range range;
        bool shared_pmd = false;

        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, old_addr,
                                old_end);
        adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
        /*
         * In case of shared PMDs, we should cover the maximum possible
         * range.
         */
        flush_cache_range(vma, range.start, range.end);

        mmu_notifier_invalidate_range_start(&range);
        last_addr_mask = hugetlb_mask_last_page(h);
        /* Prevent race with file truncation */
        hugetlb_vma_lock_write(vma);
        i_mmap_lock_write(mapping);
        for (; old_addr < old_end; old_addr += sz, new_addr += sz) {
                src_pte = hugetlb_walk(vma, old_addr, sz);
                if (!src_pte) {
                        old_addr |= last_addr_mask;
                        new_addr |= last_addr_mask;
                        continue;
                }
                if (huge_pte_none(huge_ptep_get(src_pte)))
                        continue;

                if (huge_pmd_unshare(mm, vma, old_addr, src_pte)) {
                        shared_pmd = true;
                        old_addr |= last_addr_mask;
                        new_addr |= last_addr_mask;
                        continue;
                }

                dst_pte = huge_pte_alloc(mm, new_vma, new_addr, sz);
                if (!dst_pte)
                        break;

                move_huge_pte(vma, old_addr, new_addr, src_pte, dst_pte, sz);
        }

        if (shared_pmd)
                flush_hugetlb_tlb_range(vma, range.start, range.end);
        else
                flush_hugetlb_tlb_range(vma, old_end - len, old_end);
        mmu_notifier_invalidate_range_end(&range);
        i_mmap_unlock_write(mapping);
        hugetlb_vma_unlock_write(vma);

        return len + old_addr - old_end;
}

void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
                            unsigned long start, unsigned long end,
                            struct page *ref_page, zap_flags_t zap_flags)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long address;
        pte_t *ptep;
        pte_t pte;
        spinlock_t *ptl;
        struct page *page;
        struct hstate *h = hstate_vma(vma);
        unsigned long sz = huge_page_size(h);
        bool adjust_reservation = false;
        unsigned long last_addr_mask;
        bool force_flush = false;

        WARN_ON(!is_vm_hugetlb_page(vma));
        BUG_ON(start & ~huge_page_mask(h));
        BUG_ON(end & ~huge_page_mask(h));

        /*
         * This is a hugetlb vma, all the pte entries should point
         * to huge page.
         */
        tlb_change_page_size(tlb, sz);
        tlb_start_vma(tlb, vma);

        last_addr_mask = hugetlb_mask_last_page(h);
        address = start;
        for (; address < end; address += sz) {
                ptep = hugetlb_walk(vma, address, sz);
                if (!ptep) {
                        address |= last_addr_mask;
                        continue;
                }

                ptl = huge_pte_lock(h, mm, ptep);
                if (huge_pmd_unshare(mm, vma, address, ptep)) {
                        spin_unlock(ptl);
                        tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE);
                        force_flush = true;
                        address |= last_addr_mask;
                        continue;
                }

                pte = huge_ptep_get(ptep);
                if (huge_pte_none(pte)) {
                        spin_unlock(ptl);
                        continue;
                }

                /*
                 * Migrating hugepage or HWPoisoned hugepage is already
                 * unmapped and its refcount is dropped, so just clear pte here.
                 */
                if (unlikely(!pte_present(pte))) {
                        /*
                         * If the pte was wr-protected by uffd-wp in any of the
                         * swap forms, meanwhile the caller does not want to
                         * drop the uffd-wp bit in this zap, then replace the
                         * pte with a marker.
                         */
                        if (pte_swp_uffd_wp_any(pte) &&
                            !(zap_flags & ZAP_FLAG_DROP_MARKER))
                                set_huge_pte_at(mm, address, ptep,
                                                make_pte_marker(PTE_MARKER_UFFD_WP),
                                                sz);
                        else
                                huge_pte_clear(mm, address, ptep, sz);
                        spin_unlock(ptl);
                        continue;
                }

                page = pte_page(pte);
                /*
                 * If a reference page is supplied, it is because a specific
                 * page is being unmapped, not a range. Ensure the page we
                 * are about to unmap is the actual page of interest.
                 */
                if (ref_page) {
                        if (page != ref_page) {
                                spin_unlock(ptl);
                                continue;
                        }
                        /*
                         * Mark the VMA as having unmapped its page so that
                         * future faults in this VMA will fail rather than
                         * looking like data was lost
                         */
                        set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
                }

                pte = huge_ptep_get_and_clear(mm, address, ptep);
                tlb_remove_huge_tlb_entry(h, tlb, ptep, address);
                if (huge_pte_dirty(pte))
                        set_page_dirty(page);
                /* Leave a uffd-wp pte marker if needed */
                if (huge_pte_uffd_wp(pte) &&
                    !(zap_flags & ZAP_FLAG_DROP_MARKER))
                        set_huge_pte_at(mm, address, ptep,
                                        make_pte_marker(PTE_MARKER_UFFD_WP),
                                        sz);
                hugetlb_count_sub(pages_per_huge_page(h), mm);
                hugetlb_remove_rmap(page_folio(page));

                /*
                 * Restore the reservation for anonymous page, otherwise the
                 * backing page could be stolen by someone.
                 * If there we are freeing a surplus, do not set the restore
                 * reservation bit.
                 */
                if (!h->surplus_huge_pages && __vma_private_lock(vma) &&
                    folio_test_anon(page_folio(page))) {
                        folio_set_hugetlb_restore_reserve(page_folio(page));
                        /* Reservation to be adjusted after the spin lock */
                        adjust_reservation = true;
                }

                spin_unlock(ptl);

                /*
                 * Adjust the reservation for the region that will have the
                 * reserve restored. Keep in mind that vma_needs_reservation() changes
                 * resv->adds_in_progress if it succeeds. If this is not done,
                 * do_exit() will not see it, and will keep the reservation
                 * forever.
                 */
                if (adjust_reservation && vma_needs_reservation(h, vma, address))
                        vma_add_reservation(h, vma, address);

                tlb_remove_page_size(tlb, page, huge_page_size(h));
                /*
                 * Bail out after unmapping reference page if supplied
                 */
                if (ref_page)
                        break;
        }
        tlb_end_vma(tlb, vma);

        /*
         * If we unshared PMDs, the TLB flush was not recorded in mmu_gather. We
         * could defer the flush until now, since by holding i_mmap_rwsem we
         * guaranteed that the last refernece would not be dropped. But we must
         * do the flushing before we return, as otherwise i_mmap_rwsem will be
         * dropped and the last reference to the shared PMDs page might be
         * dropped as well.
         *
         * In theory we could defer the freeing of the PMD pages as well, but
         * huge_pmd_unshare() relies on the exact page_count for the PMD page to
         * detect sharing, so we cannot defer the release of the page either.
         * Instead, do flush now.
         */
        if (force_flush)
                tlb_flush_mmu_tlbonly(tlb);
}

void __hugetlb_zap_begin(struct vm_area_struct *vma,
                         unsigned long *start, unsigned long *end)
{
        if (!vma->vm_file)      /* hugetlbfs_file_mmap error */
                return;

        adjust_range_if_pmd_sharing_possible(vma, start, end);
        hugetlb_vma_lock_write(vma);
        if (vma->vm_file)
                i_mmap_lock_write(vma->vm_file->f_mapping);
}

void __hugetlb_zap_end(struct vm_area_struct *vma,
                       struct zap_details *details)
{
        zap_flags_t zap_flags = details ? details->zap_flags : 0;

        if (!vma->vm_file)      /* hugetlbfs_file_mmap error */
                return;

        if (zap_flags & ZAP_FLAG_UNMAP) {       /* final unmap */
                /*
                 * Unlock and free the vma lock before releasing i_mmap_rwsem.
                 * When the vma_lock is freed, this makes the vma ineligible
                 * for pmd sharing.  And, i_mmap_rwsem is required to set up
                 * pmd sharing.  This is important as page tables for this
                 * unmapped range will be asynchrously deleted.  If the page
                 * tables are shared, there will be issues when accessed by
                 * someone else.
                 */
                __hugetlb_vma_unlock_write_free(vma);
        } else {
                hugetlb_vma_unlock_write(vma);
        }

        if (vma->vm_file)
                i_mmap_unlock_write(vma->vm_file->f_mapping);
}

void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
                          unsigned long end, struct page *ref_page,
                          zap_flags_t zap_flags)
{
        struct mmu_notifier_range range;
        struct mmu_gather tlb;

        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
                                start, end);
        adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);
        mmu_notifier_invalidate_range_start(&range);
        tlb_gather_mmu(&tlb, vma->vm_mm);

        __unmap_hugepage_range(&tlb, vma, start, end, ref_page, zap_flags);

        mmu_notifier_invalidate_range_end(&range);
        tlb_finish_mmu(&tlb);
}

/*
 * This is called when the original mapper is failing to COW a MAP_PRIVATE
 * mapping it owns the reserve page for. The intention is to unmap the page
 * from other VMAs and let the children be SIGKILLed if they are faulting the
 * same region.
 */
static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
                              struct page *page, unsigned long address)
{
        struct hstate *h = hstate_vma(vma);
        struct vm_area_struct *iter_vma;
        struct address_space *mapping;
        pgoff_t pgoff;

        /*
         * vm_pgoff is in PAGE_SIZE units, hence the different calculation
         * from page cache lookup which is in HPAGE_SIZE units.
         */
        address = address & huge_page_mask(h);
        pgoff = ((address - vma->vm_start) >> PAGE_SHIFT) +
                        vma->vm_pgoff;
        mapping = vma->vm_file->f_mapping;

        /*
         * Take the mapping lock for the duration of the table walk. As
         * this mapping should be shared between all the VMAs,
         * __unmap_hugepage_range() is called as the lock is already held
         */
        i_mmap_lock_write(mapping);
        vma_interval_tree_foreach(iter_vma, &mapping->i_mmap, pgoff, pgoff) {
                /* Do not unmap the current VMA */
                if (iter_vma == vma)
                        continue;

                /*
                 * Shared VMAs have their own reserves and do not affect
                 * MAP_PRIVATE accounting but it is possible that a shared
                 * VMA is using the same page so check and skip such VMAs.
                 */
                if (iter_vma->vm_flags & VM_MAYSHARE)
                        continue;

                /*
                 * Unmap the page from other VMAs without their own reserves.
                 * They get marked to be SIGKILLed if they fault in these
                 * areas. This is because a future no-page fault on this VMA
                 * could insert a zeroed page instead of the data existing
                 * from the time of fork. This would look like data corruption
                 */
                if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER))
                        unmap_hugepage_range(iter_vma, address,
                                             address + huge_page_size(h), page, 0);
        }
        i_mmap_unlock_write(mapping);
}

/*
 * hugetlb_wp() should be called with page lock of the original hugepage held.
 * Called with hugetlb_fault_mutex_table held and pte_page locked so we
 * cannot race with other handlers or page migration.
 * Keep the pte_same checks anyway to make transition from the mutex easier.
 */
static vm_fault_t hugetlb_wp(struct folio *pagecache_folio,
                       struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct mm_struct *mm = vma->vm_mm;
        const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
        pte_t pte = huge_ptep_get(vmf->pte);
        struct hstate *h = hstate_vma(vma);
        struct folio *old_folio;
        struct folio *new_folio;
        int outside_reserve = 0;
        vm_fault_t ret = 0;
        struct mmu_notifier_range range;

        /*
         * Never handle CoW for uffd-wp protected pages.  It should be only
         * handled when the uffd-wp protection is removed.
         *
         * Note that only the CoW optimization path (in hugetlb_no_page())
         * can trigger this, because hugetlb_fault() will always resolve
         * uffd-wp bit first.
         */
        if (!unshare && huge_pte_uffd_wp(pte))
                return 0;

        /*
         * hugetlb does not support FOLL_FORCE-style write faults that keep the
         * PTE mapped R/O such as maybe_mkwrite() would do.
         */
        if (WARN_ON_ONCE(!unshare && !(vma->vm_flags & VM_WRITE)))
                return VM_FAULT_SIGSEGV;

        /* Let's take out MAP_SHARED mappings first. */
        if (vma->vm_flags & VM_MAYSHARE) {
                set_huge_ptep_writable(vma, vmf->address, vmf->pte);
                return 0;
        }

        old_folio = page_folio(pte_page(pte));

        delayacct_wpcopy_start();

retry_avoidcopy:
        /*
         * If no-one else is actually using this page, we're the exclusive
         * owner and can reuse this page.
         */
        if (folio_mapcount(old_folio) == 1 && folio_test_anon(old_folio)) {
                if (!PageAnonExclusive(&old_folio->page)) {
                        folio_move_anon_rmap(old_folio, vma);
                        SetPageAnonExclusive(&old_folio->page);
                }
                if (likely(!unshare))
                        set_huge_ptep_writable(vma, vmf->address, vmf->pte);

                delayacct_wpcopy_end();
                return 0;
        }
        VM_BUG_ON_PAGE(folio_test_anon(old_folio) &&
                       PageAnonExclusive(&old_folio->page), &old_folio->page);

        /*
         * If the process that created a MAP_PRIVATE mapping is about to
         * perform a COW due to a shared page count, attempt to satisfy
         * the allocation without using the existing reserves. The pagecache
         * page is used to determine if the reserve at this address was
         * consumed or not. If reserves were used, a partial faulted mapping
         * at the time of fork() could consume its reserves on COW instead
         * of the full address range.
         */
        if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
                        old_folio != pagecache_folio)
                outside_reserve = 1;

        folio_get(old_folio);

        /*
         * Drop page table lock as buddy allocator may be called. It will
         * be acquired again before returning to the caller, as expected.
         */
        spin_unlock(vmf->ptl);
        new_folio = alloc_hugetlb_folio(vma, vmf->address, outside_reserve);

        if (IS_ERR(new_folio)) {
                /*
                 * If a process owning a MAP_PRIVATE mapping fails to COW,
                 * it is due to references held by a child and an insufficient
                 * huge page pool. To guarantee the original mappers
                 * reliability, unmap the page from child processes. The child
                 * may get SIGKILLed if it later faults.
                 */
                if (outside_reserve) {
                        struct address_space *mapping = vma->vm_file->f_mapping;
                        pgoff_t idx;
                        u32 hash;

                        folio_put(old_folio);
                        /*
                         * Drop hugetlb_fault_mutex and vma_lock before
                         * unmapping.  unmapping needs to hold vma_lock
                         * in write mode.  Dropping vma_lock in read mode
                         * here is OK as COW mappings do not interact with
                         * PMD sharing.
                         *
                         * Reacquire both after unmap operation.
                         */
                        idx = vma_hugecache_offset(h, vma, vmf->address);
                        hash = hugetlb_fault_mutex_hash(mapping, idx);
                        hugetlb_vma_unlock_read(vma);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);

                        unmap_ref_private(mm, vma, &old_folio->page,
                                        vmf->address);

                        mutex_lock(&hugetlb_fault_mutex_table[hash]);
                        hugetlb_vma_lock_read(vma);
                        spin_lock(vmf->ptl);
                        vmf->pte = hugetlb_walk(vma, vmf->address,
                                        huge_page_size(h));
                        if (likely(vmf->pte &&
                                   pte_same(huge_ptep_get(vmf->pte), pte)))
                                goto retry_avoidcopy;
                        /*
                         * race occurs while re-acquiring page table
                         * lock, and our job is done.
                         */
                        delayacct_wpcopy_end();
                        return 0;
                }

                ret = vmf_error(PTR_ERR(new_folio));
                goto out_release_old;
        }

        /*
         * When the original hugepage is shared one, it does not have
         * anon_vma prepared.
         */
        ret = vmf_anon_prepare(vmf);
        if (unlikely(ret))
                goto out_release_all;

        if (copy_user_large_folio(new_folio, old_folio, vmf->real_address, vma)) {
                ret = VM_FAULT_HWPOISON_LARGE;
                goto out_release_all;
        }
        __folio_mark_uptodate(new_folio);

        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, vmf->address,
                                vmf->address + huge_page_size(h));
        mmu_notifier_invalidate_range_start(&range);

        /*
         * Retake the page table lock to check for racing updates
         * before the page tables are altered
         */
        spin_lock(vmf->ptl);
        vmf->pte = hugetlb_walk(vma, vmf->address, huge_page_size(h));
        if (likely(vmf->pte && pte_same(huge_ptep_get(vmf->pte), pte))) {
                pte_t newpte = make_huge_pte(vma, &new_folio->page, !unshare);

                /* Break COW or unshare */
                huge_ptep_clear_flush(vma, vmf->address, vmf->pte);
                hugetlb_remove_rmap(old_folio);
                hugetlb_add_new_anon_rmap(new_folio, vma, vmf->address);
                if (huge_pte_uffd_wp(pte))
                        newpte = huge_pte_mkuffd_wp(newpte);
                set_huge_pte_at(mm, vmf->address, vmf->pte, newpte,
                                huge_page_size(h));
                folio_set_hugetlb_migratable(new_folio);
                /* Make the old page be freed below */
                new_folio = old_folio;
        }
        spin_unlock(vmf->ptl);
        mmu_notifier_invalidate_range_end(&range);
out_release_all:
        /*
         * No restore in case of successful pagetable update (Break COW or
         * unshare)
         */
        if (new_folio != old_folio)
                restore_reserve_on_error(h, vma, vmf->address, new_folio);
        folio_put(new_folio);
out_release_old:
        folio_put(old_folio);

        spin_lock(vmf->ptl); /* Caller expects lock to be held */

        delayacct_wpcopy_end();
        return ret;
}

/*
 * Return whether there is a pagecache page to back given address within VMA.
 */
bool hugetlbfs_pagecache_present(struct hstate *h,
                                 struct vm_area_struct *vma, unsigned long address)
{
        struct address_space *mapping = vma->vm_file->f_mapping;
        pgoff_t idx = linear_page_index(vma, address);
        struct folio *folio;

        folio = filemap_get_folio(mapping, idx);
        if (IS_ERR(folio))
                return false;
        folio_put(folio);
        return true;
}

int hugetlb_add_to_page_cache(struct folio *folio, struct address_space *mapping,
                           pgoff_t idx)
{
        struct inode *inode = mapping->host;
        struct hstate *h = hstate_inode(inode);
        int err;

        idx <<= huge_page_order(h);
        __folio_set_locked(folio);
        err = __filemap_add_folio(mapping, folio, idx, GFP_KERNEL, NULL);

        if (unlikely(err)) {
                __folio_clear_locked(folio);
                return err;
        }
        folio_clear_hugetlb_restore_reserve(folio);

        /*
         * mark folio dirty so that it will not be removed from cache/file
         * by non-hugetlbfs specific code paths.
         */
        folio_mark_dirty(folio);

        spin_lock(&inode->i_lock);
        inode->i_blocks += blocks_per_huge_page(h);
        spin_unlock(&inode->i_lock);
        return 0;
}

static inline vm_fault_t hugetlb_handle_userfault(struct vm_fault *vmf,
                                                  struct address_space *mapping,
                                                  unsigned long reason)
{
        u32 hash;

        /*
         * vma_lock and hugetlb_fault_mutex must be dropped before handling
         * userfault. Also mmap_lock could be dropped due to handling
         * userfault, any vma operation should be careful from here.
         */
        hugetlb_vma_unlock_read(vmf->vma);
        hash = hugetlb_fault_mutex_hash(mapping, vmf->pgoff);
        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
        return handle_userfault(vmf, reason);
}

/*
 * Recheck pte with pgtable lock.  Returns true if pte didn't change, or
 * false if pte changed or is changing.
 */
static bool hugetlb_pte_stable(struct hstate *h, struct mm_struct *mm,
                               pte_t *ptep, pte_t old_pte)
{
        spinlock_t *ptl;
        bool same;

        ptl = huge_pte_lock(h, mm, ptep);
        same = pte_same(huge_ptep_get(ptep), old_pte);
        spin_unlock(ptl);

        return same;
}

static vm_fault_t hugetlb_no_page(struct address_space *mapping,
                        struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct mm_struct *mm = vma->vm_mm;
        struct hstate *h = hstate_vma(vma);
        vm_fault_t ret = VM_FAULT_SIGBUS;
        int anon_rmap = 0;
        unsigned long size;
        struct folio *folio;
        pte_t new_pte;
        bool new_folio, new_pagecache_folio = false;
        u32 hash = hugetlb_fault_mutex_hash(mapping, vmf->pgoff);

        /*
         * Currently, we are forced to kill the process in the event the
         * original mapper has unmapped pages from the child due to a failed
         * COW/unsharing. Warn that such a situation has occurred as it may not
         * be obvious.
         */
        if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {
                pr_warn_ratelimited("PID %d killed due to inadequate hugepage pool\n",
                           current->pid);
                goto out;
        }

        /*
         * Use page lock to guard against racing truncation
         * before we get page_table_lock.
         */
        new_folio = false;
        folio = filemap_lock_hugetlb_folio(h, mapping, vmf->pgoff);
        if (IS_ERR(folio)) {
                size = i_size_read(mapping->host) >> huge_page_shift(h);
                if (vmf->pgoff >= size)
                        goto out;
                /* Check for page in userfault range */
                if (userfaultfd_missing(vma)) {
                        /*
                         * Since hugetlb_no_page() was examining pte
                         * without pgtable lock, we need to re-test under
                         * lock because the pte may not be stable and could
                         * have changed from under us.  Try to detect
                         * either changed or during-changing ptes and retry
                         * properly when needed.
                         *
                         * Note that userfaultfd is actually fine with
                         * false positives (e.g. caused by pte changed),
                         * but not wrong logical events (e.g. caused by
                         * reading a pte during changing).  The latter can
                         * confuse the userspace, so the strictness is very
                         * much preferred.  E.g., MISSING event should
                         * never happen on the page after UFFDIO_COPY has
                         * correctly installed the page and returned.
                         */
                        if (!hugetlb_pte_stable(h, mm, vmf->pte, vmf->orig_pte)) {
                                ret = 0;
                                goto out;
                        }

                        return hugetlb_handle_userfault(vmf, mapping,
                                                        VM_UFFD_MISSING);
                }

                if (!(vma->vm_flags & VM_MAYSHARE)) {
                        ret = vmf_anon_prepare(vmf);
                        if (unlikely(ret))
                                goto out;
                }

                folio = alloc_hugetlb_folio(vma, vmf->address, 0);
                if (IS_ERR(folio)) {
                        /*
                         * Returning error will result in faulting task being
                         * sent SIGBUS.  The hugetlb fault mutex prevents two
                         * tasks from racing to fault in the same page which
                         * could result in false unable to allocate errors.
                         * Page migration does not take the fault mutex, but
                         * does a clear then write of pte's under page table
                         * lock.  Page fault code could race with migration,
                         * notice the clear pte and try to allocate a page
                         * here.  Before returning error, get ptl and make
                         * sure there really is no pte entry.
                         */
                        if (hugetlb_pte_stable(h, mm, vmf->pte, vmf->orig_pte))
                                ret = vmf_error(PTR_ERR(folio));
                        else
                                ret = 0;
                        goto out;
                }
                clear_huge_page(&folio->page, vmf->real_address,
                                pages_per_huge_page(h));
                __folio_mark_uptodate(folio);
                new_folio = true;

                if (vma->vm_flags & VM_MAYSHARE) {
                        int err = hugetlb_add_to_page_cache(folio, mapping,
                                                        vmf->pgoff);
                        if (err) {
                                /*
                                 * err can't be -EEXIST which implies someone
                                 * else consumed the reservation since hugetlb
                                 * fault mutex is held when add a hugetlb page
                                 * to the page cache. So it's safe to call
                                 * restore_reserve_on_error() here.
                                 */
                                restore_reserve_on_error(h, vma, vmf->address,
                                                        folio);
                                folio_put(folio);
                                ret = VM_FAULT_SIGBUS;
                                goto out;
                        }
                        new_pagecache_folio = true;
                } else {
                        folio_lock(folio);
                        anon_rmap = 1;
                }
        } else {
                /*
                 * If memory error occurs between mmap() and fault, some process
                 * don't have hwpoisoned swap entry for errored virtual address.
                 * So we need to block hugepage fault by PG_hwpoison bit check.
                 */
                if (unlikely(folio_test_hwpoison(folio))) {
                        ret = VM_FAULT_HWPOISON_LARGE |
                                VM_FAULT_SET_HINDEX(hstate_index(h));
                        goto backout_unlocked;
                }

                /* Check for page in userfault range. */
                if (userfaultfd_minor(vma)) {
                        folio_unlock(folio);
                        folio_put(folio);
                        /* See comment in userfaultfd_missing() block above */
                        if (!hugetlb_pte_stable(h, mm, vmf->pte, vmf->orig_pte)) {
                                ret = 0;
                                goto out;
                        }
                        return hugetlb_handle_userfault(vmf, mapping,
                                                        VM_UFFD_MINOR);
                }
        }

        /*
         * If we are going to COW a private mapping later, we examine the
         * pending reservations for this page now. This will ensure that
         * any allocations necessary to record that reservation occur outside
         * the spinlock.
         */
        if ((vmf->flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
                if (vma_needs_reservation(h, vma, vmf->address) < 0) {
                        ret = VM_FAULT_OOM;
                        goto backout_unlocked;
                }
                /* Just decrements count, does not deallocate */
                vma_end_reservation(h, vma, vmf->address);
        }

        vmf->ptl = huge_pte_lock(h, mm, vmf->pte);
        ret = 0;
        /* If pte changed from under us, retry */
        if (!pte_same(huge_ptep_get(vmf->pte), vmf->orig_pte))
                goto backout;

        if (anon_rmap)
                hugetlb_add_new_anon_rmap(folio, vma, vmf->address);
        else
                hugetlb_add_file_rmap(folio);
        new_pte = make_huge_pte(vma, &folio->page, ((vma->vm_flags & VM_WRITE)
                                && (vma->vm_flags & VM_SHARED)));
        /*
         * If this pte was previously wr-protected, keep it wr-protected even
         * if populated.
         */
        if (unlikely(pte_marker_uffd_wp(vmf->orig_pte)))
                new_pte = huge_pte_mkuffd_wp(new_pte);
        set_huge_pte_at(mm, vmf->address, vmf->pte, new_pte, huge_page_size(h));

        hugetlb_count_add(pages_per_huge_page(h), mm);
        if ((vmf->flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
                /* Optimization, do the COW without a second fault */
                ret = hugetlb_wp(folio, vmf);
        }

        spin_unlock(vmf->ptl);

        /*
         * Only set hugetlb_migratable in newly allocated pages.  Existing pages
         * found in the pagecache may not have hugetlb_migratable if they have
         * been isolated for migration.
         */
        if (new_folio)
                folio_set_hugetlb_migratable(folio);

        folio_unlock(folio);
out:
        hugetlb_vma_unlock_read(vma);
        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
        return ret;

backout:
        spin_unlock(vmf->ptl);
backout_unlocked:
        if (new_folio && !new_pagecache_folio)
                restore_reserve_on_error(h, vma, vmf->address, folio);

        folio_unlock(folio);
        folio_put(folio);
        goto out;
}

#ifdef CONFIG_SMP
u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx)
{
        unsigned long key[2];
        u32 hash;

        key[0] = (unsigned long) mapping;
        key[1] = idx;

        hash = jhash2((u32 *)&key, sizeof(key)/(sizeof(u32)), 0);

        return hash & (num_fault_mutexes - 1);
}
#else
/*
 * For uniprocessor systems we always use a single mutex, so just
 * return 0 and avoid the hashing overhead.
 */
u32 hugetlb_fault_mutex_hash(struct address_space *mapping, pgoff_t idx)
{
        return 0;
}
#endif

vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long address, unsigned int flags)
{
        vm_fault_t ret;
        u32 hash;
        struct folio *folio = NULL;
        struct folio *pagecache_folio = NULL;
        struct hstate *h = hstate_vma(vma);
        struct address_space *mapping;
        int need_wait_lock = 0;
        struct vm_fault vmf = {
                .vma = vma,
                .address = address & huge_page_mask(h),
                .real_address = address,
                .flags = flags,
                .pgoff = vma_hugecache_offset(h, vma,
                                address & huge_page_mask(h)),
                /* TODO: Track hugetlb faults using vm_fault */

                /*
                 * Some fields may not be initialized, be careful as it may
                 * be hard to debug if called functions make assumptions
                 */
        };

        /*
         * Serialize hugepage allocation and instantiation, so that we don't
         * get spurious allocation failures if two CPUs race to instantiate
         * the same page in the page cache.
         */
        mapping = vma->vm_file->f_mapping;
        hash = hugetlb_fault_mutex_hash(mapping, vmf.pgoff);
        mutex_lock(&hugetlb_fault_mutex_table[hash]);

        /*
         * Acquire vma lock before calling huge_pte_alloc and hold
         * until finished with vmf.pte.  This prevents huge_pmd_unshare from
         * being called elsewhere and making the vmf.pte no longer valid.
         */
        hugetlb_vma_lock_read(vma);
        vmf.pte = huge_pte_alloc(mm, vma, vmf.address, huge_page_size(h));
        if (!vmf.pte) {
                hugetlb_vma_unlock_read(vma);
                mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                return VM_FAULT_OOM;
        }

        vmf.orig_pte = huge_ptep_get(vmf.pte);
        if (huge_pte_none_mostly(vmf.orig_pte)) {
                if (is_pte_marker(vmf.orig_pte)) {
                        pte_marker marker =
                                pte_marker_get(pte_to_swp_entry(vmf.orig_pte));

                        if (marker & PTE_MARKER_POISONED) {
                                ret = VM_FAULT_HWPOISON_LARGE;
                                goto out_mutex;
                        }
                }

                /*
                 * Other PTE markers should be handled the same way as none PTE.
                 *
                 * hugetlb_no_page will drop vma lock and hugetlb fault
                 * mutex internally, which make us return immediately.
                 */
                return hugetlb_no_page(mapping, &vmf);
        }

        ret = 0;

        /*
         * vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
         * point, so this check prevents the kernel from going below assuming
         * that we have an active hugepage in pagecache. This goto expects
         * the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned)
         * check will properly handle it.
         */
        if (!pte_present(vmf.orig_pte)) {
                if (unlikely(is_hugetlb_entry_migration(vmf.orig_pte))) {
                        /*
                         * Release the hugetlb fault lock now, but retain
                         * the vma lock, because it is needed to guard the
                         * huge_pte_lockptr() later in
                         * migration_entry_wait_huge(). The vma lock will
                         * be released there.
                         */
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        migration_entry_wait_huge(vma, vmf.pte);
                        return 0;
                } else if (unlikely(is_hugetlb_entry_hwpoisoned(vmf.orig_pte)))
                        ret = VM_FAULT_HWPOISON_LARGE |
                            VM_FAULT_SET_HINDEX(hstate_index(h));
                goto out_mutex;
        }

        /*
         * If we are going to COW/unshare the mapping later, we examine the
         * pending reservations for this page now. This will ensure that any
         * allocations necessary to record that reservation occur outside the
         * spinlock. Also lookup the pagecache page now as it is used to
         * determine if a reservation has been consumed.
         */
        if ((flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) &&
            !(vma->vm_flags & VM_MAYSHARE) && !huge_pte_write(vmf.orig_pte)) {
                if (vma_needs_reservation(h, vma, vmf.address) < 0) {
                        ret = VM_FAULT_OOM;
                        goto out_mutex;
                }
                /* Just decrements count, does not deallocate */
                vma_end_reservation(h, vma, vmf.address);

                pagecache_folio = filemap_lock_hugetlb_folio(h, mapping,
                                                             vmf.pgoff);
                if (IS_ERR(pagecache_folio))
                        pagecache_folio = NULL;
        }

        vmf.ptl = huge_pte_lock(h, mm, vmf.pte);

        /* Check for a racing update before calling hugetlb_wp() */
        if (unlikely(!pte_same(vmf.orig_pte, huge_ptep_get(vmf.pte))))
                goto out_ptl;

        /* Handle userfault-wp first, before trying to lock more pages */
        if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(vmf.pte)) &&
            (flags & FAULT_FLAG_WRITE) && !huge_pte_write(vmf.orig_pte)) {
                if (!userfaultfd_wp_async(vma)) {
                        spin_unlock(vmf.ptl);
                        if (pagecache_folio) {
                                folio_unlock(pagecache_folio);
                                folio_put(pagecache_folio);
                        }
                        hugetlb_vma_unlock_read(vma);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        return handle_userfault(&vmf, VM_UFFD_WP);
                }

                vmf.orig_pte = huge_pte_clear_uffd_wp(vmf.orig_pte);
                set_huge_pte_at(mm, vmf.address, vmf.pte, vmf.orig_pte,
                                huge_page_size(hstate_vma(vma)));
                /* Fallthrough to CoW */
        }

        /*
         * hugetlb_wp() requires page locks of pte_page(vmf.orig_pte) and
         * pagecache_folio, so here we need take the former one
         * when folio != pagecache_folio or !pagecache_folio.
         */
        folio = page_folio(pte_page(vmf.orig_pte));
        if (folio != pagecache_folio)
                if (!folio_trylock(folio)) {
                        need_wait_lock = 1;
                        goto out_ptl;
                }

        folio_get(folio);

        if (flags & (FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE)) {
                if (!huge_pte_write(vmf.orig_pte)) {
                        ret = hugetlb_wp(pagecache_folio, &vmf);
                        goto out_put_page;
                } else if (likely(flags & FAULT_FLAG_WRITE)) {
                        vmf.orig_pte = huge_pte_mkdirty(vmf.orig_pte);
                }
        }
        vmf.orig_pte = pte_mkyoung(vmf.orig_pte);
        if (huge_ptep_set_access_flags(vma, vmf.address, vmf.pte, vmf.orig_pte,
                                                flags & FAULT_FLAG_WRITE))
                update_mmu_cache(vma, vmf.address, vmf.pte);
out_put_page:
        if (folio != pagecache_folio)
                folio_unlock(folio);
        folio_put(folio);
out_ptl:
        spin_unlock(vmf.ptl);

        if (pagecache_folio) {
                folio_unlock(pagecache_folio);
                folio_put(pagecache_folio);
        }
out_mutex:
        hugetlb_vma_unlock_read(vma);
        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
        /*
         * Generally it's safe to hold refcount during waiting page lock. But
         * here we just wait to defer the next page fault to avoid busy loop and
         * the page is not used after unlocked before returning from the current
         * page fault. So we are safe from accessing freed page, even if we wait
         * here without taking refcount.
         */
        if (need_wait_lock)
                folio_wait_locked(folio);
        return ret;
}

#ifdef CONFIG_USERFAULTFD
/*
 * Can probably be eliminated, but still used by hugetlb_mfill_atomic_pte().
 */
static struct folio *alloc_hugetlb_folio_vma(struct hstate *h,
                struct vm_area_struct *vma, unsigned long address)
{
        struct mempolicy *mpol;
        nodemask_t *nodemask;
        struct folio *folio;
        gfp_t gfp_mask;
        int node;

        gfp_mask = htlb_alloc_mask(h);
        node = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
        /*
         * This is used to allocate a temporary hugetlb to hold the copied
         * content, which will then be copied again to the final hugetlb
         * consuming a reservation. Set the alloc_fallback to false to indicate
         * that breaking the per-node hugetlb pool is not allowed in this case.
         */
        folio = alloc_hugetlb_folio_nodemask(h, node, nodemask, gfp_mask, false);
        mpol_cond_put(mpol);

        return folio;
}

/*
 * Used by userfaultfd UFFDIO_* ioctls. Based on userfaultfd's mfill_atomic_pte
 * with modifications for hugetlb pages.
 */
int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
                             struct vm_area_struct *dst_vma,
                             unsigned long dst_addr,
                             unsigned long src_addr,
                             uffd_flags_t flags,
                             struct folio **foliop)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        bool is_continue = uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE);
        bool wp_enabled = (flags & MFILL_ATOMIC_WP);
        struct hstate *h = hstate_vma(dst_vma);
        struct address_space *mapping = dst_vma->vm_file->f_mapping;
        pgoff_t idx = vma_hugecache_offset(h, dst_vma, dst_addr);
        unsigned long size;
        int vm_shared = dst_vma->vm_flags & VM_SHARED;
        pte_t _dst_pte;
        spinlock_t *ptl;
        int ret = -ENOMEM;
        struct folio *folio;
        int writable;
        bool folio_in_pagecache = false;

        if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
                ptl = huge_pte_lock(h, dst_mm, dst_pte);

                /* Don't overwrite any existing PTEs (even markers) */
                if (!huge_pte_none(huge_ptep_get(dst_pte))) {
                        spin_unlock(ptl);
                        return -EEXIST;
                }

                _dst_pte = make_pte_marker(PTE_MARKER_POISONED);
                set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte,
                                huge_page_size(h));

                /* No need to invalidate - it was non-present before */
                update_mmu_cache(dst_vma, dst_addr, dst_pte);

                spin_unlock(ptl);
                return 0;
        }

        if (is_continue) {
                ret = -EFAULT;
                folio = filemap_lock_hugetlb_folio(h, mapping, idx);
                if (IS_ERR(folio))
                        goto out;
                folio_in_pagecache = true;
        } else if (!*foliop) {
                /* If a folio already exists, then it's UFFDIO_COPY for
                 * a non-missing case. Return -EEXIST.
                 */
                if (vm_shared &&
                    hugetlbfs_pagecache_present(h, dst_vma, dst_addr)) {
                        ret = -EEXIST;
                        goto out;
                }

                folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0);
                if (IS_ERR(folio)) {
                        ret = -ENOMEM;
                        goto out;
                }

                ret = copy_folio_from_user(folio, (const void __user *) src_addr,
                                           false);

                /* fallback to copy_from_user outside mmap_lock */
                if (unlikely(ret)) {
                        ret = -ENOENT;
                        /* Free the allocated folio which may have
                         * consumed a reservation.
                         */
                        restore_reserve_on_error(h, dst_vma, dst_addr, folio);
                        folio_put(folio);

                        /* Allocate a temporary folio to hold the copied
                         * contents.
                         */
                        folio = alloc_hugetlb_folio_vma(h, dst_vma, dst_addr);
                        if (!folio) {
                                ret = -ENOMEM;
                                goto out;
                        }
                        *foliop = folio;
                        /* Set the outparam foliop and return to the caller to
                         * copy the contents outside the lock. Don't free the
                         * folio.
                         */
                        goto out;
                }
        } else {
                if (vm_shared &&
                    hugetlbfs_pagecache_present(h, dst_vma, dst_addr)) {
                        folio_put(*foliop);
                        ret = -EEXIST;
                        *foliop = NULL;
                        goto out;
                }

                folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0);
                if (IS_ERR(folio)) {
                        folio_put(*foliop);
                        ret = -ENOMEM;
                        *foliop = NULL;
                        goto out;
                }
                ret = copy_user_large_folio(folio, *foliop, dst_addr, dst_vma);
                folio_put(*foliop);
                *foliop = NULL;
                if (ret) {
                        folio_put(folio);
                        goto out;
                }
        }

        /*
         * If we just allocated a new page, we need a memory barrier to ensure
         * that preceding stores to the page become visible before the
         * set_pte_at() write. The memory barrier inside __folio_mark_uptodate
         * is what we need.
         *
         * In the case where we have not allocated a new page (is_continue),
         * the page must already be uptodate. UFFDIO_CONTINUE already includes
         * an earlier smp_wmb() to ensure that prior stores will be visible
         * before the set_pte_at() write.
         */
        if (!is_continue)
                __folio_mark_uptodate(folio);
        else
                WARN_ON_ONCE(!folio_test_uptodate(folio));

        /* Add shared, newly allocated pages to the page cache. */
        if (vm_shared && !is_continue) {
                size = i_size_read(mapping->host) >> huge_page_shift(h);
                ret = -EFAULT;
                if (idx >= size)
                        goto out_release_nounlock;

                /*
                 * Serialization between remove_inode_hugepages() and
                 * hugetlb_add_to_page_cache() below happens through the
                 * hugetlb_fault_mutex_table that here must be hold by
                 * the caller.
                 */
                ret = hugetlb_add_to_page_cache(folio, mapping, idx);
                if (ret)
                        goto out_release_nounlock;
                folio_in_pagecache = true;
        }

        ptl = huge_pte_lock(h, dst_mm, dst_pte);

        ret = -EIO;
        if (folio_test_hwpoison(folio))
                goto out_release_unlock;

        /*
         * We allow to overwrite a pte marker: consider when both MISSING|WP
         * registered, we firstly wr-protect a none pte which has no page cache
         * page backing it, then access the page.
         */
        ret = -EEXIST;
        if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
                goto out_release_unlock;

        if (folio_in_pagecache)
                hugetlb_add_file_rmap(folio);
        else
                hugetlb_add_new_anon_rmap(folio, dst_vma, dst_addr);

        /*
         * For either: (1) CONTINUE on a non-shared VMA, or (2) UFFDIO_COPY
         * with wp flag set, don't set pte write bit.
         */
        if (wp_enabled || (is_continue && !vm_shared))
                writable = 0;
        else
                writable = dst_vma->vm_flags & VM_WRITE;

        _dst_pte = make_huge_pte(dst_vma, &folio->page, writable);
        /*
         * Always mark UFFDIO_COPY page dirty; note that this may not be
         * extremely important for hugetlbfs for now since swapping is not
         * supported, but we should still be clear in that this page cannot be
         * thrown away at will, even if write bit not set.
         */
        _dst_pte = huge_pte_mkdirty(_dst_pte);
        _dst_pte = pte_mkyoung(_dst_pte);

        if (wp_enabled)
                _dst_pte = huge_pte_mkuffd_wp(_dst_pte);

        set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte, huge_page_size(h));

        hugetlb_count_add(pages_per_huge_page(h), dst_mm);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(dst_vma, dst_addr, dst_pte);

        spin_unlock(ptl);
        if (!is_continue)
                folio_set_hugetlb_migratable(folio);
        if (vm_shared || is_continue)
                folio_unlock(folio);
        ret = 0;
out:
        return ret;
out_release_unlock:
        spin_unlock(ptl);
        if (vm_shared || is_continue)
                folio_unlock(folio);
out_release_nounlock:
        if (!folio_in_pagecache)
                restore_reserve_on_error(h, dst_vma, dst_addr, folio);
        folio_put(folio);
        goto out;
}
#endif /* CONFIG_USERFAULTFD */

long hugetlb_change_protection(struct vm_area_struct *vma,
                unsigned long address, unsigned long end,
                pgprot_t newprot, unsigned long cp_flags)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long start = address;
        pte_t *ptep;
        pte_t pte;
        struct hstate *h = hstate_vma(vma);
        long pages = 0, psize = huge_page_size(h);
        bool shared_pmd = false;
        struct mmu_notifier_range range;
        unsigned long last_addr_mask;
        bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
        bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;

        /*
         * In the case of shared PMDs, the area to flush could be beyond
         * start/end.  Set range.start/range.end to cover the maximum possible
         * range if PMD sharing is possible.
         */
        mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA,
                                0, mm, start, end);
        adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end);

        BUG_ON(address >= end);
        flush_cache_range(vma, range.start, range.end);

        mmu_notifier_invalidate_range_start(&range);
        hugetlb_vma_lock_write(vma);
        i_mmap_lock_write(vma->vm_file->f_mapping);
        last_addr_mask = hugetlb_mask_last_page(h);
        for (; address < end; address += psize) {
                spinlock_t *ptl;
                ptep = hugetlb_walk(vma, address, psize);
                if (!ptep) {
                        if (!uffd_wp) {
                                address |= last_addr_mask;
                                continue;
                        }
                        /*
                         * Userfaultfd wr-protect requires pgtable
                         * pre-allocations to install pte markers.
                         */
                        ptep = huge_pte_alloc(mm, vma, address, psize);
                        if (!ptep) {
                                pages = -ENOMEM;
                                break;
                        }
                }
                ptl = huge_pte_lock(h, mm, ptep);
                if (huge_pmd_unshare(mm, vma, address, ptep)) {
                        /*
                         * When uffd-wp is enabled on the vma, unshare
                         * shouldn't happen at all.  Warn about it if it
                         * happened due to some reason.
                         */
                        WARN_ON_ONCE(uffd_wp || uffd_wp_resolve);
                        pages++;
                        spin_unlock(ptl);
                        shared_pmd = true;
                        address |= last_addr_mask;
                        continue;
                }
                pte = huge_ptep_get(ptep);
                if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
                        /* Nothing to do. */
                } else if (unlikely(is_hugetlb_entry_migration(pte))) {
                        swp_entry_t entry = pte_to_swp_entry(pte);
                        struct page *page = pfn_swap_entry_to_page(entry);
                        pte_t newpte = pte;

                        if (is_writable_migration_entry(entry)) {
                                if (PageAnon(page))
                                        entry = make_readable_exclusive_migration_entry(
                                                                swp_offset(entry));
                                else
                                        entry = make_readable_migration_entry(
                                                                swp_offset(entry));
                                newpte = swp_entry_to_pte(entry);
                                pages++;
                        }

                        if (uffd_wp)
                                newpte = pte_swp_mkuffd_wp(newpte);
                        else if (uffd_wp_resolve)
                                newpte = pte_swp_clear_uffd_wp(newpte);
                        if (!pte_same(pte, newpte))
                                set_huge_pte_at(mm, address, ptep, newpte, psize);
                } else if (unlikely(is_pte_marker(pte))) {
                        /*
                         * Do nothing on a poison marker; page is
                         * corrupted, permissons do not apply.  Here
                         * pte_marker_uffd_wp()==true implies !poison
                         * because they're mutual exclusive.
                         */
                        if (pte_marker_uffd_wp(pte) && uffd_wp_resolve)
                                /* Safe to modify directly (non-present->none). */
                                huge_pte_clear(mm, address, ptep, psize);
                } else if (!huge_pte_none(pte)) {
                        pte_t old_pte;
                        unsigned int shift = huge_page_shift(hstate_vma(vma));

                        old_pte = huge_ptep_modify_prot_start(vma, address, ptep);
                        pte = huge_pte_modify(old_pte, newprot);
                        pte = arch_make_huge_pte(pte, shift, vma->vm_flags);
                        if (uffd_wp)
                                pte = huge_pte_mkuffd_wp(pte);
                        else if (uffd_wp_resolve)
                                pte = huge_pte_clear_uffd_wp(pte);
                        huge_ptep_modify_prot_commit(vma, address, ptep, old_pte, pte);
                        pages++;
                } else {
                        /* None pte */
                        if (unlikely(uffd_wp))
                                /* Safe to modify directly (none->non-present). */
                                set_huge_pte_at(mm, address, ptep,
                                                make_pte_marker(PTE_MARKER_UFFD_WP),
                                                psize);
                }
                spin_unlock(ptl);
        }
        /*
         * Must flush TLB before releasing i_mmap_rwsem: x86's huge_pmd_unshare
         * may have cleared our pud entry and done put_page on the page table:
         * once we release i_mmap_rwsem, another task can do the final put_page
         * and that page table be reused and filled with junk.  If we actually
         * did unshare a page of pmds, flush the range corresponding to the pud.
         */
        if (shared_pmd)
                flush_hugetlb_tlb_range(vma, range.start, range.end);
        else
                flush_hugetlb_tlb_range(vma, start, end);
        /*
         * No need to call mmu_notifier_arch_invalidate_secondary_tlbs() we are
         * downgrading page table protection not changing it to point to a new
         * page.
         *
         * See Documentation/mm/mmu_notifier.rst
         */
        i_mmap_unlock_write(vma->vm_file->f_mapping);
        hugetlb_vma_unlock_write(vma);
        mmu_notifier_invalidate_range_end(&range);

        return pages > 0 ? (pages << h->order) : pages;
}

/* Return true if reservation was successful, false otherwise.  */
bool hugetlb_reserve_pages(struct inode *inode,
                                        long from, long to,
                                        struct vm_area_struct *vma,
                                        vm_flags_t vm_flags)
{
        long chg = -1, add = -1;
        struct hstate *h = hstate_inode(inode);
        struct hugepage_subpool *spool = subpool_inode(inode);
        struct resv_map *resv_map;
        struct hugetlb_cgroup *h_cg = NULL;
        long gbl_reserve, regions_needed = 0;

        /* This should never happen */
        if (from > to) {
                VM_WARN(1, "%s called with a negative range\n", __func__);
                return false;
        }

        /*
         * vma specific semaphore used for pmd sharing and fault/truncation
         * synchronization
         */
        hugetlb_vma_lock_alloc(vma);

        /*
         * Only apply hugepage reservation if asked. At fault time, an
         * attempt will be made for VM_NORESERVE to allocate a page
         * without using reserves
         */
        if (vm_flags & VM_NORESERVE)
                return true;

        /*
         * Shared mappings base their reservation on the number of pages that
         * are already allocated on behalf of the file. Private mappings need
         * to reserve the full area even if read-only as mprotect() may be
         * called to make the mapping read-write. Assume !vma is a shm mapping
         */
        if (!vma || vma->vm_flags & VM_MAYSHARE) {
                /*
                 * resv_map can not be NULL as hugetlb_reserve_pages is only
                 * called for inodes for which resv_maps were created (see
                 * hugetlbfs_get_inode).
                 */
                resv_map = inode_resv_map(inode);

                chg = region_chg(resv_map, from, to, &regions_needed);
        } else {
                /* Private mapping. */
                resv_map = resv_map_alloc();
                if (!resv_map)
                        goto out_err;

                chg = to - from;

                set_vma_resv_map(vma, resv_map);
                set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
        }

        if (chg < 0)
                goto out_err;

        if (hugetlb_cgroup_charge_cgroup_rsvd(hstate_index(h),
                                chg * pages_per_huge_page(h), &h_cg) < 0)
                goto out_err;

        if (vma && !(vma->vm_flags & VM_MAYSHARE) && h_cg) {
                /* For private mappings, the hugetlb_cgroup uncharge info hangs
                 * of the resv_map.
                 */
                resv_map_set_hugetlb_cgroup_uncharge_info(resv_map, h_cg, h);
        }

        /*
         * There must be enough pages in the subpool for the mapping. If
         * the subpool has a minimum size, there may be some global
         * reservations already in place (gbl_reserve).
         */
        gbl_reserve = hugepage_subpool_get_pages(spool, chg);
        if (gbl_reserve < 0)
                goto out_uncharge_cgroup;

        /*
         * Check enough hugepages are available for the reservation.
         * Hand the pages back to the subpool if there are not
         */
        if (hugetlb_acct_memory(h, gbl_reserve) < 0)
                goto out_put_pages;

        /*
         * Account for the reservations made. Shared mappings record regions
         * that have reservations as they are shared by multiple VMAs.
         * When the last VMA disappears, the region map says how much
         * the reservation was and the page cache tells how much of
         * the reservation was consumed. Private mappings are per-VMA and
         * only the consumed reservations are tracked. When the VMA
         * disappears, the original reservation is the VMA size and the
         * consumed reservations are stored in the map. Hence, nothing
         * else has to be done for private mappings here
         */
        if (!vma || vma->vm_flags & VM_MAYSHARE) {
                add = region_add(resv_map, from, to, regions_needed, h, h_cg);

                if (unlikely(add < 0)) {
                        hugetlb_acct_memory(h, -gbl_reserve);
                        goto out_put_pages;
                } else if (unlikely(chg > add)) {
                        /*
                         * pages in this range were added to the reserve
                         * map between region_chg and region_add.  This
                         * indicates a race with alloc_hugetlb_folio.  Adjust
                         * the subpool and reserve counts modified above
                         * based on the difference.
                         */
                        long rsv_adjust;

                        /*
                         * hugetlb_cgroup_uncharge_cgroup_rsvd() will put the
                         * reference to h_cg->css. See comment below for detail.
                         */
                        hugetlb_cgroup_uncharge_cgroup_rsvd(
                                hstate_index(h),
                                (chg - add) * pages_per_huge_page(h), h_cg);

                        rsv_adjust = hugepage_subpool_put_pages(spool,
                                                                chg - add);
                        hugetlb_acct_memory(h, -rsv_adjust);
                } else if (h_cg) {
                        /*
                         * The file_regions will hold their own reference to
                         * h_cg->css. So we should release the reference held
                         * via hugetlb_cgroup_charge_cgroup_rsvd() when we are
                         * done.
                         */
                        hugetlb_cgroup_put_rsvd_cgroup(h_cg);
                }
        }
        return true;

out_put_pages:
        /* put back original number of pages, chg */
        (void)hugepage_subpool_put_pages(spool, chg);
out_uncharge_cgroup:
        hugetlb_cgroup_uncharge_cgroup_rsvd(hstate_index(h),
                                            chg * pages_per_huge_page(h), h_cg);
out_err:
        hugetlb_vma_lock_free(vma);
        if (!vma || vma->vm_flags & VM_MAYSHARE)
                /* Only call region_abort if the region_chg succeeded but the
                 * region_add failed or didn't run.
                 */
                if (chg >= 0 && add < 0)
                        region_abort(resv_map, from, to, regions_needed);
        if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) {
                kref_put(&resv_map->refs, resv_map_release);
                set_vma_resv_map(vma, NULL);
        }
        return false;
}

long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
                                                                long freed)
{
        struct hstate *h = hstate_inode(inode);
        struct resv_map *resv_map = inode_resv_map(inode);
        long chg = 0;
        struct hugepage_subpool *spool = subpool_inode(inode);
        long gbl_reserve;

        /*
         * Since this routine can be called in the evict inode path for all
         * hugetlbfs inodes, resv_map could be NULL.
         */
        if (resv_map) {
                chg = region_del(resv_map, start, end);
                /*
                 * region_del() can fail in the rare case where a region
                 * must be split and another region descriptor can not be
                 * allocated.  If end == LONG_MAX, it will not fail.
                 */
                if (chg < 0)
                        return chg;
        }

        spin_lock(&inode->i_lock);
        inode->i_blocks -= (blocks_per_huge_page(h) * freed);
        spin_unlock(&inode->i_lock);

        /*
         * If the subpool has a minimum size, the number of global
         * reservations to be released may be adjusted.
         *
         * Note that !resv_map implies freed == 0. So (chg - freed)
         * won't go negative.
         */
        gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed));
        hugetlb_acct_memory(h, -gbl_reserve);

        return 0;
}

#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
static unsigned long page_table_shareable(struct vm_area_struct *svma,
                                struct vm_area_struct *vma,
                                unsigned long addr, pgoff_t idx)
{
        unsigned long saddr = ((idx - svma->vm_pgoff) << PAGE_SHIFT) +
                                svma->vm_start;
        unsigned long sbase = saddr & PUD_MASK;
        unsigned long s_end = sbase + PUD_SIZE;

        /* Allow segments to share if only one is marked locked */
        unsigned long vm_flags = vma->vm_flags & ~VM_LOCKED_MASK;
        unsigned long svm_flags = svma->vm_flags & ~VM_LOCKED_MASK;

        /*
         * match the virtual addresses, permission and the alignment of the
         * page table page.
         *
         * Also, vma_lock (vm_private_data) is required for sharing.
         */
        if (pmd_index(addr) != pmd_index(saddr) ||
            vm_flags != svm_flags ||
            !range_in_vma(svma, sbase, s_end) ||
            !svma->vm_private_data)
                return 0;

        return saddr;
}

bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr)
{
        unsigned long start = addr & PUD_MASK;
        unsigned long end = start + PUD_SIZE;

#ifdef CONFIG_USERFAULTFD
        if (uffd_disable_huge_pmd_share(vma))
                return false;
#endif
        /*
         * check on proper vm_flags and page table alignment
         */
        if (!(vma->vm_flags & VM_MAYSHARE))
                return false;
        if (!vma->vm_private_data)      /* vma lock required for sharing */
                return false;
        if (!range_in_vma(vma, start, end))
                return false;
        return true;
}

/*
 * Determine if start,end range within vma could be mapped by shared pmd.
 * If yes, adjust start and end to cover range associated with possible
 * shared pmd mappings.
 */
void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
                                unsigned long *start, unsigned long *end)
{
        unsigned long v_start = ALIGN(vma->vm_start, PUD_SIZE),
                v_end = ALIGN_DOWN(vma->vm_end, PUD_SIZE);

        /*
         * vma needs to span at least one aligned PUD size, and the range
         * must be at least partially within in.
         */
        if (!(vma->vm_flags & VM_MAYSHARE) || !(v_end > v_start) ||
                (*end <= v_start) || (*start >= v_end))
                return;

        /* Extend the range to be PUD aligned for a worst case scenario */
        if (*start > v_start)
                *start = ALIGN_DOWN(*start, PUD_SIZE);

        if (*end < v_end)
                *end = ALIGN(*end, PUD_SIZE);
}

/*
 * Search for a shareable pmd page for hugetlb. In any case calls pmd_alloc()
 * and returns the corresponding pte. While this is not necessary for the
 * !shared pmd case because we can allocate the pmd later as well, it makes the
 * code much cleaner. pmd allocation is essential for the shared case because
 * pud has to be populated inside the same i_mmap_rwsem section - otherwise
 * racing tasks could either miss the sharing (see huge_pte_offset) or select a
 * bad pmd for sharing.
 */
pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
                      unsigned long addr, pud_t *pud)
{
        struct address_space *mapping = vma->vm_file->f_mapping;
        pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
                        vma->vm_pgoff;
        struct vm_area_struct *svma;
        unsigned long saddr;
        pte_t *spte = NULL;
        pte_t *pte;

        i_mmap_lock_read(mapping);
        vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {
                if (svma == vma)
                        continue;

                saddr = page_table_shareable(svma, vma, addr, idx);
                if (saddr) {
                        spte = hugetlb_walk(svma, saddr,
                                            vma_mmu_pagesize(svma));
                        if (spte) {
                                get_page(virt_to_page(spte));
                                break;
                        }
                }
        }

        if (!spte)
                goto out;

        spin_lock(&mm->page_table_lock);
        if (pud_none(*pud)) {
                pud_populate(mm, pud,
                                (pmd_t *)((unsigned long)spte & PAGE_MASK));
                mm_inc_nr_pmds(mm);
        } else {
                put_page(virt_to_page(spte));
        }
        spin_unlock(&mm->page_table_lock);
out:
        pte = (pte_t *)pmd_alloc(mm, pud, addr);
        i_mmap_unlock_read(mapping);
        return pte;
}

/*
 * unmap huge page backed by shared pte.
 *
 * Hugetlb pte page is ref counted at the time of mapping.  If pte is shared
 * indicated by page_count > 1, unmap is achieved by clearing pud and
 * decrementing the ref count. If count == 1, the pte page is not shared.
 *
 * Called with page table lock held.
 *
 * returns: 1 successfully unmapped a shared pte page
 *          0 the underlying pte page is not shared, or it is the last user
 */
int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
                                        unsigned long addr, pte_t *ptep)
{
        pgd_t *pgd = pgd_offset(mm, addr);
        p4d_t *p4d = p4d_offset(pgd, addr);
        pud_t *pud = pud_offset(p4d, addr);

        i_mmap_assert_write_locked(vma->vm_file->f_mapping);
        hugetlb_vma_assert_locked(vma);
        BUG_ON(page_count(virt_to_page(ptep)) == 0);
        if (page_count(virt_to_page(ptep)) == 1)
                return 0;

        pud_clear(pud);
        put_page(virt_to_page(ptep));
        mm_dec_nr_pmds(mm);
        return 1;
}

#else /* !CONFIG_ARCH_WANT_HUGE_PMD_SHARE */

pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
                      unsigned long addr, pud_t *pud)
{
        return NULL;
}

int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
                                unsigned long addr, pte_t *ptep)
{
        return 0;
}

void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
                                unsigned long *start, unsigned long *end)
{
}

bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr)
{
        return false;
}
#endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */

#ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long addr, unsigned long sz)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pte_t *pte = NULL;

        pgd = pgd_offset(mm, addr);
        p4d = p4d_alloc(mm, pgd, addr);
        if (!p4d)
                return NULL;
        pud = pud_alloc(mm, p4d, addr);
        if (pud) {
                if (sz == PUD_SIZE) {
                        pte = (pte_t *)pud;
                } else {
                        BUG_ON(sz != PMD_SIZE);
                        if (want_pmd_share(vma, addr) && pud_none(*pud))
                                pte = huge_pmd_share(mm, vma, addr, pud);
                        else
                                pte = (pte_t *)pmd_alloc(mm, pud, addr);
                }
        }

        if (pte) {
                pte_t pteval = ptep_get_lockless(pte);

                BUG_ON(pte_present(pteval) && !pte_huge(pteval));
        }

        return pte;
}

/*
 * huge_pte_offset() - Walk the page table to resolve the hugepage
 * entry at address @addr
 *
 * Return: Pointer to page table entry (PUD or PMD) for
 * address @addr, or NULL if a !p*d_present() entry is encountered and the
 * size @sz doesn't match the hugepage size at this level of the page
 * table.
 */
pte_t *huge_pte_offset(struct mm_struct *mm,
                       unsigned long addr, unsigned long sz)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;

        pgd = pgd_offset(mm, addr);
        if (!pgd_present(*pgd))
                return NULL;
        p4d = p4d_offset(pgd, addr);
        if (!p4d_present(*p4d))
                return NULL;

        pud = pud_offset(p4d, addr);
        if (sz == PUD_SIZE)
                /* must be pud huge, non-present or none */
                return (pte_t *)pud;
        if (!pud_present(*pud))
                return NULL;
        /* must have a valid entry and size to go further */

        pmd = pmd_offset(pud, addr);
        /* must be pmd huge, non-present or none */
        return (pte_t *)pmd;
}

/*
 * Return a mask that can be used to update an address to the last huge
 * page in a page table page mapping size.  Used to skip non-present
 * page table entries when linearly scanning address ranges.  Architectures
 * with unique huge page to page table relationships can define their own
 * version of this routine.
 */
unsigned long hugetlb_mask_last_page(struct hstate *h)
{
        unsigned long hp_size = huge_page_size(h);

        if (hp_size == PUD_SIZE)
                return P4D_SIZE - PUD_SIZE;
        else if (hp_size == PMD_SIZE)
                return PUD_SIZE - PMD_SIZE;
        else
                return 0UL;
}

#else

/* See description above.  Architectures can provide their own version. */
__weak unsigned long hugetlb_mask_last_page(struct hstate *h)
{
#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
        if (huge_page_size(h) == PMD_SIZE)
                return PUD_SIZE - PMD_SIZE;
#endif
        return 0UL;
}

#endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */

/*
 * These functions are overwritable if your architecture needs its own
 * behavior.
 */
bool isolate_hugetlb(struct folio *folio, struct list_head *list)
{
        bool ret = true;

        spin_lock_irq(&hugetlb_lock);
        if (!folio_test_hugetlb(folio) ||
            !folio_test_hugetlb_migratable(folio) ||
            !folio_try_get(folio)) {
                ret = false;
                goto unlock;
        }
        folio_clear_hugetlb_migratable(folio);
        list_move_tail(&folio->lru, list);
unlock:
        spin_unlock_irq(&hugetlb_lock);
        return ret;
}

int get_hwpoison_hugetlb_folio(struct folio *folio, bool *hugetlb, bool unpoison)
{
        int ret = 0;

        *hugetlb = false;
        spin_lock_irq(&hugetlb_lock);
        if (folio_test_hugetlb(folio)) {
                *hugetlb = true;
                if (folio_test_hugetlb_freed(folio))
                        ret = 0;
                else if (folio_test_hugetlb_migratable(folio) || unpoison)
                        ret = folio_try_get(folio);
                else
                        ret = -EBUSY;
        }
        spin_unlock_irq(&hugetlb_lock);
        return ret;
}

int get_huge_page_for_hwpoison(unsigned long pfn, int flags,
                                bool *migratable_cleared)
{
        int ret;

        spin_lock_irq(&hugetlb_lock);
        ret = __get_huge_page_for_hwpoison(pfn, flags, migratable_cleared);
        spin_unlock_irq(&hugetlb_lock);
        return ret;
}

void folio_putback_active_hugetlb(struct folio *folio)
{
        spin_lock_irq(&hugetlb_lock);
        folio_set_hugetlb_migratable(folio);
        list_move_tail(&folio->lru, &(folio_hstate(folio))->hugepage_activelist);
        spin_unlock_irq(&hugetlb_lock);
        folio_put(folio);
}

void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int reason)
{
        struct hstate *h = folio_hstate(old_folio);

        hugetlb_cgroup_migrate(old_folio, new_folio);
        set_page_owner_migrate_reason(&new_folio->page, reason);

        /*
         * transfer temporary state of the new hugetlb folio. This is
         * reverse to other transitions because the newpage is going to
         * be final while the old one will be freed so it takes over
         * the temporary status.
         *
         * Also note that we have to transfer the per-node surplus state
         * here as well otherwise the global surplus count will not match
         * the per-node's.
         */
        if (folio_test_hugetlb_temporary(new_folio)) {
                int old_nid = folio_nid(old_folio);
                int new_nid = folio_nid(new_folio);

                folio_set_hugetlb_temporary(old_folio);
                folio_clear_hugetlb_temporary(new_folio);


                /*
                 * There is no need to transfer the per-node surplus state
                 * when we do not cross the node.
                 */
                if (new_nid == old_nid)
                        return;
                spin_lock_irq(&hugetlb_lock);
                if (h->surplus_huge_pages_node[old_nid]) {
                        h->surplus_huge_pages_node[old_nid]--;
                        h->surplus_huge_pages_node[new_nid]++;
                }
                spin_unlock_irq(&hugetlb_lock);
        }
}

static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
                                   unsigned long start,
                                   unsigned long end)
{
        struct hstate *h = hstate_vma(vma);
        unsigned long sz = huge_page_size(h);
        struct mm_struct *mm = vma->vm_mm;
        struct mmu_notifier_range range;
        unsigned long address;
        spinlock_t *ptl;
        pte_t *ptep;

        if (!(vma->vm_flags & VM_MAYSHARE))
                return;

        if (start >= end)
                return;

        flush_cache_range(vma, start, end);
        /*
         * No need to call adjust_range_if_pmd_sharing_possible(), because
         * we have already done the PUD_SIZE alignment.
         */
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
                                start, end);
        mmu_notifier_invalidate_range_start(&range);
        hugetlb_vma_lock_write(vma);
        i_mmap_lock_write(vma->vm_file->f_mapping);
        for (address = start; address < end; address += PUD_SIZE) {
                ptep = hugetlb_walk(vma, address, sz);
                if (!ptep)
                        continue;
                ptl = huge_pte_lock(h, mm, ptep);
                huge_pmd_unshare(mm, vma, address, ptep);
                spin_unlock(ptl);
        }
        flush_hugetlb_tlb_range(vma, start, end);
        i_mmap_unlock_write(vma->vm_file->f_mapping);
        hugetlb_vma_unlock_write(vma);
        /*
         * No need to call mmu_notifier_arch_invalidate_secondary_tlbs(), see
         * Documentation/mm/mmu_notifier.rst.
         */
        mmu_notifier_invalidate_range_end(&range);
}

/*
 * This function will unconditionally remove all the shared pmd pgtable entries
 * within the specific vma for a hugetlbfs memory range.
 */
void hugetlb_unshare_all_pmds(struct vm_area_struct *vma)
{
        hugetlb_unshare_pmds(vma, ALIGN(vma->vm_start, PUD_SIZE),
                        ALIGN_DOWN(vma->vm_end, PUD_SIZE));
}

#ifdef CONFIG_CMA
static bool cma_reserve_called __initdata;

static int __init cmdline_parse_hugetlb_cma(char *p)
{
        int nid, count = 0;
        unsigned long tmp;
        char *s = p;

        while (*s) {
                if (sscanf(s, "%lu%n", &tmp, &count) != 1)
                        break;

                if (s[count] == ':') {
                        if (tmp >= MAX_NUMNODES)
                                break;
                        nid = array_index_nospec(tmp, MAX_NUMNODES);

                        s += count + 1;
                        tmp = memparse(s, &s);
                        hugetlb_cma_size_in_node[nid] = tmp;
                        hugetlb_cma_size += tmp;

                        /*
                         * Skip the separator if have one, otherwise
                         * break the parsing.
                         */
                        if (*s == ',')
                                s++;
                        else
                                break;
                } else {
                        hugetlb_cma_size = memparse(p, &p);
                        break;
                }
        }

        return 0;
}

early_param("hugetlb_cma", cmdline_parse_hugetlb_cma);

void __init hugetlb_cma_reserve(int order)
{
        unsigned long size, reserved, per_node;
        bool node_specific_cma_alloc = false;
        int nid;

        /*
         * HugeTLB CMA reservation is required for gigantic
         * huge pages which could not be allocated via the
         * page allocator. Just warn if there is any change
         * breaking this assumption.
         */
        VM_WARN_ON(order <= MAX_PAGE_ORDER);
        cma_reserve_called = true;

        if (!hugetlb_cma_size)
                return;

        for (nid = 0; nid < MAX_NUMNODES; nid++) {
                if (hugetlb_cma_size_in_node[nid] == 0)
                        continue;

                if (!node_online(nid)) {
                        pr_warn("hugetlb_cma: invalid node %d specified\n", nid);
                        hugetlb_cma_size -= hugetlb_cma_size_in_node[nid];
                        hugetlb_cma_size_in_node[nid] = 0;
                        continue;
                }

                if (hugetlb_cma_size_in_node[nid] < (PAGE_SIZE << order)) {
                        pr_warn("hugetlb_cma: cma area of node %d should be at least %lu MiB\n",
                                nid, (PAGE_SIZE << order) / SZ_1M);
                        hugetlb_cma_size -= hugetlb_cma_size_in_node[nid];
                        hugetlb_cma_size_in_node[nid] = 0;
                } else {
                        node_specific_cma_alloc = true;
                }
        }

        /* Validate the CMA size again in case some invalid nodes specified. */
        if (!hugetlb_cma_size)
                return;

        if (hugetlb_cma_size < (PAGE_SIZE << order)) {
                pr_warn("hugetlb_cma: cma area should be at least %lu MiB\n",
                        (PAGE_SIZE << order) / SZ_1M);
                hugetlb_cma_size = 0;
                return;
        }

        if (!node_specific_cma_alloc) {
                /*
                 * If 3 GB area is requested on a machine with 4 numa nodes,
                 * let's allocate 1 GB on first three nodes and ignore the last one.
                 */
                per_node = DIV_ROUND_UP(hugetlb_cma_size, nr_online_nodes);
                pr_info("hugetlb_cma: reserve %lu MiB, up to %lu MiB per node\n",
                        hugetlb_cma_size / SZ_1M, per_node / SZ_1M);
        }

        reserved = 0;
        for_each_online_node(nid) {
                int res;
                char name[CMA_MAX_NAME];

                if (node_specific_cma_alloc) {
                        if (hugetlb_cma_size_in_node[nid] == 0)
                                continue;

                        size = hugetlb_cma_size_in_node[nid];
                } else {
                        size = min(per_node, hugetlb_cma_size - reserved);
                }

                size = round_up(size, PAGE_SIZE << order);

                snprintf(name, sizeof(name), "hugetlb%d", nid);
                /*
                 * Note that 'order per bit' is based on smallest size that
                 * may be returned to CMA allocator in the case of
                 * huge page demotion.
                 */
                res = cma_declare_contiguous_nid(0, size, 0,
                                        PAGE_SIZE << HUGETLB_PAGE_ORDER,
                                        HUGETLB_PAGE_ORDER, false, name,
                                        &hugetlb_cma[nid], nid);
                if (res) {
                        pr_warn("hugetlb_cma: reservation failed: err %d, node %d",
                                res, nid);
                        continue;
                }

                reserved += size;
                pr_info("hugetlb_cma: reserved %lu MiB on node %d\n",
                        size / SZ_1M, nid);

                if (reserved >= hugetlb_cma_size)
                        break;
        }

        if (!reserved)
                /*
                 * hugetlb_cma_size is used to determine if allocations from
                 * cma are possible.  Set to zero if no cma regions are set up.
                 */
                hugetlb_cma_size = 0;
}

static void __init hugetlb_cma_check(void)
{
        if (!hugetlb_cma_size || cma_reserve_called)
                return;

        pr_warn("hugetlb_cma: the option isn't supported by current arch\n");
}

#endif /* CONFIG_CMA */