Merge tag 'nfs-for-6.10-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs

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

// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code        <alan@lxorguk.ukuu.org.uk>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/capability.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/profile.h>
#include <linux/export.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/mmdebug.h>
#include <linux/perf_event.h>
#include <linux/audit.h>
#include <linux/khugepaged.h>
#include <linux/uprobes.h>
#include <linux/notifier.h>
#include <linux/memory.h>
#include <linux/printk.h>
#include <linux/userfaultfd_k.h>
#include <linux/moduleparam.h>
#include <linux/pkeys.h>
#include <linux/oom.h>
#include <linux/sched/mm.h>
#include <linux/ksm.h>

#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlb.h>
#include <asm/mmu_context.h>

#define CREATE_TRACE_POINTS
#include <trace/events/mmap.h>

#include "internal.h"

#ifndef arch_mmap_check
#define arch_mmap_check(addr, len, flags)       (0)
#endif

#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
int mmap_rnd_bits_max __ro_after_init = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
#endif

static bool ignore_rlimit_data;
core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);

static void unmap_region(struct mm_struct *mm, struct ma_state *mas,
                struct vm_area_struct *vma, struct vm_area_struct *prev,
                struct vm_area_struct *next, unsigned long start,
                unsigned long end, unsigned long tree_end, bool mm_wr_locked);

static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
{
        return pgprot_modify(oldprot, vm_get_page_prot(vm_flags));
}

/* Update vma->vm_page_prot to reflect vma->vm_flags. */
void vma_set_page_prot(struct vm_area_struct *vma)
{
        unsigned long vm_flags = vma->vm_flags;
        pgprot_t vm_page_prot;

        vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
        if (vma_wants_writenotify(vma, vm_page_prot)) {
                vm_flags &= ~VM_SHARED;
                vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
        }
        /* remove_protection_ptes reads vma->vm_page_prot without mmap_lock */
        WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}

/*
 * Requires inode->i_mapping->i_mmap_rwsem
 */
static void __remove_shared_vm_struct(struct vm_area_struct *vma,
                                      struct address_space *mapping)
{
        if (vma_is_shared_maywrite(vma))
                mapping_unmap_writable(mapping);

        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_remove(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

/*
 * Unlink a file-based vm structure from its interval tree, to hide
 * vma from rmap and vmtruncate before freeing its page tables.
 */
void unlink_file_vma(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;

        if (file) {
                struct address_space *mapping = file->f_mapping;
                i_mmap_lock_write(mapping);
                __remove_shared_vm_struct(vma, mapping);
                i_mmap_unlock_write(mapping);
        }
}

/*
 * Close a vm structure and free it.
 */
static void remove_vma(struct vm_area_struct *vma, bool unreachable)
{
        might_sleep();
        if (vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);
        if (vma->vm_file)
                fput(vma->vm_file);
        mpol_put(vma_policy(vma));
        if (unreachable)
                __vm_area_free(vma);
        else
                vm_area_free(vma);
}

static inline struct vm_area_struct *vma_prev_limit(struct vma_iterator *vmi,
                                                    unsigned long min)
{
        return mas_prev(&vmi->mas, min);
}

/*
 * check_brk_limits() - Use platform specific check of range & verify mlock
 * limits.
 * @addr: The address to check
 * @len: The size of increase.
 *
 * Return: 0 on success.
 */
static int check_brk_limits(unsigned long addr, unsigned long len)
{
        unsigned long mapped_addr;

        mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
        if (IS_ERR_VALUE(mapped_addr))
                return mapped_addr;

        return mlock_future_ok(current->mm, current->mm->def_flags, len)
                ? 0 : -EAGAIN;
}
static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *brkvma,
                unsigned long addr, unsigned long request, unsigned long flags);
SYSCALL_DEFINE1(brk, unsigned long, brk)
{
        unsigned long newbrk, oldbrk, origbrk;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *brkvma, *next = NULL;
        unsigned long min_brk;
        bool populate = false;
        LIST_HEAD(uf);
        struct vma_iterator vmi;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        origbrk = mm->brk;

#ifdef CONFIG_COMPAT_BRK
        /*
         * CONFIG_COMPAT_BRK can still be overridden by setting
         * randomize_va_space to 2, which will still cause mm->start_brk
         * to be arbitrarily shifted
         */
        if (current->brk_randomized)
                min_brk = mm->start_brk;
        else
                min_brk = mm->end_data;
#else
        min_brk = mm->start_brk;
#endif
        if (brk < min_brk)
                goto out;

        /*
         * Check against rlimit here. If this check is done later after the test
         * of oldbrk with newbrk then it can escape the test and let the data
         * segment grow beyond its set limit the in case where the limit is
         * not page aligned -Ram Gupta
         */
        if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
                              mm->end_data, mm->start_data))
                goto out;

        newbrk = PAGE_ALIGN(brk);
        oldbrk = PAGE_ALIGN(mm->brk);
        if (oldbrk == newbrk) {
                mm->brk = brk;
                goto success;
        }

        /* Always allow shrinking brk. */
        if (brk <= mm->brk) {
                /* Search one past newbrk */
                vma_iter_init(&vmi, mm, newbrk);
                brkvma = vma_find(&vmi, oldbrk);
                if (!brkvma || brkvma->vm_start >= oldbrk)
                        goto out; /* mapping intersects with an existing non-brk vma. */
                /*
                 * mm->brk must be protected by write mmap_lock.
                 * do_vma_munmap() will drop the lock on success,  so update it
                 * before calling do_vma_munmap().
                 */
                mm->brk = brk;
                if (do_vma_munmap(&vmi, brkvma, newbrk, oldbrk, &uf, true))
                        goto out;

                goto success_unlocked;
        }

        if (check_brk_limits(oldbrk, newbrk - oldbrk))
                goto out;

        /*
         * Only check if the next VMA is within the stack_guard_gap of the
         * expansion area
         */
        vma_iter_init(&vmi, mm, oldbrk);
        next = vma_find(&vmi, newbrk + PAGE_SIZE + stack_guard_gap);
        if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
                goto out;

        brkvma = vma_prev_limit(&vmi, mm->start_brk);
        /* Ok, looks good - let it rip. */
        if (do_brk_flags(&vmi, brkvma, oldbrk, newbrk - oldbrk, 0) < 0)
                goto out;

        mm->brk = brk;
        if (mm->def_flags & VM_LOCKED)
                populate = true;

success:
        mmap_write_unlock(mm);
success_unlocked:
        userfaultfd_unmap_complete(mm, &uf);
        if (populate)
                mm_populate(oldbrk, newbrk - oldbrk);
        return brk;

out:
        mm->brk = origbrk;
        mmap_write_unlock(mm);
        return origbrk;
}

#if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
static void validate_mm(struct mm_struct *mm)
{
        int bug = 0;
        int i = 0;
        struct vm_area_struct *vma;
        VMA_ITERATOR(vmi, mm, 0);

        mt_validate(&mm->mm_mt);
        for_each_vma(vmi, vma) {
#ifdef CONFIG_DEBUG_VM_RB
                struct anon_vma *anon_vma = vma->anon_vma;
                struct anon_vma_chain *avc;
#endif
                unsigned long vmi_start, vmi_end;
                bool warn = 0;

                vmi_start = vma_iter_addr(&vmi);
                vmi_end = vma_iter_end(&vmi);
                if (VM_WARN_ON_ONCE_MM(vma->vm_end != vmi_end, mm))
                        warn = 1;

                if (VM_WARN_ON_ONCE_MM(vma->vm_start != vmi_start, mm))
                        warn = 1;

                if (warn) {
                        pr_emerg("issue in %s\n", current->comm);
                        dump_stack();
                        dump_vma(vma);
                        pr_emerg("tree range: %px start %lx end %lx\n", vma,
                                 vmi_start, vmi_end - 1);
                        vma_iter_dump_tree(&vmi);
                }

#ifdef CONFIG_DEBUG_VM_RB
                if (anon_vma) {
                        anon_vma_lock_read(anon_vma);
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                anon_vma_interval_tree_verify(avc);
                        anon_vma_unlock_read(anon_vma);
                }
#endif
                i++;
        }
        if (i != mm->map_count) {
                pr_emerg("map_count %d vma iterator %d\n", mm->map_count, i);
                bug = 1;
        }
        VM_BUG_ON_MM(bug, mm);
}

#else /* !CONFIG_DEBUG_VM_MAPLE_TREE */
#define validate_mm(mm) do { } while (0)
#endif /* CONFIG_DEBUG_VM_MAPLE_TREE */

/*
 * vma has some anon_vma assigned, and is already inserted on that
 * anon_vma's interval trees.
 *
 * Before updating the vma's vm_start / vm_end / vm_pgoff fields, the
 * vma must be removed from the anon_vma's interval trees using
 * anon_vma_interval_tree_pre_update_vma().
 *
 * After the update, the vma will be reinserted using
 * anon_vma_interval_tree_post_update_vma().
 *
 * The entire update must be protected by exclusive mmap_lock and by
 * the root anon_vma's mutex.
 */
static inline void
anon_vma_interval_tree_pre_update_vma(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc;

        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                anon_vma_interval_tree_remove(avc, &avc->anon_vma->rb_root);
}

static inline void
anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
{
        struct anon_vma_chain *avc;

        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
}

static unsigned long count_vma_pages_range(struct mm_struct *mm,
                unsigned long addr, unsigned long end)
{
        VMA_ITERATOR(vmi, mm, addr);
        struct vm_area_struct *vma;
        unsigned long nr_pages = 0;

        for_each_vma_range(vmi, vma, end) {
                unsigned long vm_start = max(addr, vma->vm_start);
                unsigned long vm_end = min(end, vma->vm_end);

                nr_pages += PHYS_PFN(vm_end - vm_start);
        }

        return nr_pages;
}

static void __vma_link_file(struct vm_area_struct *vma,
                            struct address_space *mapping)
{
        if (vma_is_shared_maywrite(vma))
                mapping_allow_writable(mapping);

        flush_dcache_mmap_lock(mapping);
        vma_interval_tree_insert(vma, &mapping->i_mmap);
        flush_dcache_mmap_unlock(mapping);
}

static void vma_link_file(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;
        struct address_space *mapping;

        if (file) {
                mapping = file->f_mapping;
                i_mmap_lock_write(mapping);
                __vma_link_file(vma, mapping);
                i_mmap_unlock_write(mapping);
        }
}

static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
{
        VMA_ITERATOR(vmi, mm, 0);

        vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        vma_start_write(vma);
        vma_iter_store(&vmi, vma);
        vma_link_file(vma);
        mm->map_count++;
        validate_mm(mm);
        return 0;
}

/*
 * init_multi_vma_prep() - Initializer for struct vma_prepare
 * @vp: The vma_prepare struct
 * @vma: The vma that will be altered once locked
 * @next: The next vma if it is to be adjusted
 * @remove: The first vma to be removed
 * @remove2: The second vma to be removed
 */
static inline void init_multi_vma_prep(struct vma_prepare *vp,
                struct vm_area_struct *vma, struct vm_area_struct *next,
                struct vm_area_struct *remove, struct vm_area_struct *remove2)
{
        memset(vp, 0, sizeof(struct vma_prepare));
        vp->vma = vma;
        vp->anon_vma = vma->anon_vma;
        vp->remove = remove;
        vp->remove2 = remove2;
        vp->adj_next = next;
        if (!vp->anon_vma && next)
                vp->anon_vma = next->anon_vma;

        vp->file = vma->vm_file;
        if (vp->file)
                vp->mapping = vma->vm_file->f_mapping;

}

/*
 * init_vma_prep() - Initializer wrapper for vma_prepare struct
 * @vp: The vma_prepare struct
 * @vma: The vma that will be altered once locked
 */
static inline void init_vma_prep(struct vma_prepare *vp,
                                 struct vm_area_struct *vma)
{
        init_multi_vma_prep(vp, vma, NULL, NULL, NULL);
}


/*
 * vma_prepare() - Helper function for handling locking VMAs prior to altering
 * @vp: The initialized vma_prepare struct
 */
static inline void vma_prepare(struct vma_prepare *vp)
{
        if (vp->file) {
                uprobe_munmap(vp->vma, vp->vma->vm_start, vp->vma->vm_end);

                if (vp->adj_next)
                        uprobe_munmap(vp->adj_next, vp->adj_next->vm_start,
                                      vp->adj_next->vm_end);

                i_mmap_lock_write(vp->mapping);
                if (vp->insert && vp->insert->vm_file) {
                        /*
                         * Put into interval tree now, so instantiated pages
                         * are visible to arm/parisc __flush_dcache_page
                         * throughout; but we cannot insert into address
                         * space until vma start or end is updated.
                         */
                        __vma_link_file(vp->insert,
                                        vp->insert->vm_file->f_mapping);
                }
        }

        if (vp->anon_vma) {
                anon_vma_lock_write(vp->anon_vma);
                anon_vma_interval_tree_pre_update_vma(vp->vma);
                if (vp->adj_next)
                        anon_vma_interval_tree_pre_update_vma(vp->adj_next);
        }

        if (vp->file) {
                flush_dcache_mmap_lock(vp->mapping);
                vma_interval_tree_remove(vp->vma, &vp->mapping->i_mmap);
                if (vp->adj_next)
                        vma_interval_tree_remove(vp->adj_next,
                                                 &vp->mapping->i_mmap);
        }

}

/*
 * vma_complete- Helper function for handling the unlocking after altering VMAs,
 * or for inserting a VMA.
 *
 * @vp: The vma_prepare struct
 * @vmi: The vma iterator
 * @mm: The mm_struct
 */
static inline void vma_complete(struct vma_prepare *vp,
                                struct vma_iterator *vmi, struct mm_struct *mm)
{
        if (vp->file) {
                if (vp->adj_next)
                        vma_interval_tree_insert(vp->adj_next,
                                                 &vp->mapping->i_mmap);
                vma_interval_tree_insert(vp->vma, &vp->mapping->i_mmap);
                flush_dcache_mmap_unlock(vp->mapping);
        }

        if (vp->remove && vp->file) {
                __remove_shared_vm_struct(vp->remove, vp->mapping);
                if (vp->remove2)
                        __remove_shared_vm_struct(vp->remove2, vp->mapping);
        } else if (vp->insert) {
                /*
                 * split_vma has split insert from vma, and needs
                 * us to insert it before dropping the locks
                 * (it may either follow vma or precede it).
                 */
                vma_iter_store(vmi, vp->insert);
                mm->map_count++;
        }

        if (vp->anon_vma) {
                anon_vma_interval_tree_post_update_vma(vp->vma);
                if (vp->adj_next)
                        anon_vma_interval_tree_post_update_vma(vp->adj_next);
                anon_vma_unlock_write(vp->anon_vma);
        }

        if (vp->file) {
                i_mmap_unlock_write(vp->mapping);
                uprobe_mmap(vp->vma);

                if (vp->adj_next)
                        uprobe_mmap(vp->adj_next);
        }

        if (vp->remove) {
again:
                vma_mark_detached(vp->remove, true);
                if (vp->file) {
                        uprobe_munmap(vp->remove, vp->remove->vm_start,
                                      vp->remove->vm_end);
                        fput(vp->file);
                }
                if (vp->remove->anon_vma)
                        anon_vma_merge(vp->vma, vp->remove);
                mm->map_count--;
                mpol_put(vma_policy(vp->remove));
                if (!vp->remove2)
                        WARN_ON_ONCE(vp->vma->vm_end < vp->remove->vm_end);
                vm_area_free(vp->remove);

                /*
                 * In mprotect's case 6 (see comments on vma_merge),
                 * we are removing both mid and next vmas
                 */
                if (vp->remove2) {
                        vp->remove = vp->remove2;
                        vp->remove2 = NULL;
                        goto again;
                }
        }
        if (vp->insert && vp->file)
                uprobe_mmap(vp->insert);
        validate_mm(mm);
}

/*
 * dup_anon_vma() - Helper function to duplicate anon_vma
 * @dst: The destination VMA
 * @src: The source VMA
 * @dup: Pointer to the destination VMA when successful.
 *
 * Returns: 0 on success.
 */
static inline int dup_anon_vma(struct vm_area_struct *dst,
                struct vm_area_struct *src, struct vm_area_struct **dup)
{
        /*
         * Easily overlooked: when mprotect shifts the boundary, make sure the
         * expanding vma has anon_vma set if the shrinking vma had, to cover any
         * anon pages imported.
         */
        if (src->anon_vma && !dst->anon_vma) {
                int ret;

                vma_assert_write_locked(dst);
                dst->anon_vma = src->anon_vma;
                ret = anon_vma_clone(dst, src);
                if (ret)
                        return ret;

                *dup = dst;
        }

        return 0;
}

/*
 * vma_expand - Expand an existing VMA
 *
 * @vmi: The vma iterator
 * @vma: The vma to expand
 * @start: The start of the vma
 * @end: The exclusive end of the vma
 * @pgoff: The page offset of vma
 * @next: The current of next vma.
 *
 * Expand @vma to @start and @end.  Can expand off the start and end.  Will
 * expand over @next if it's different from @vma and @end == @next->vm_end.
 * Checking if the @vma can expand and merge with @next needs to be handled by
 * the caller.
 *
 * Returns: 0 on success
 */
int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
               unsigned long start, unsigned long end, pgoff_t pgoff,
               struct vm_area_struct *next)
{
        struct vm_area_struct *anon_dup = NULL;
        bool remove_next = false;
        struct vma_prepare vp;

        vma_start_write(vma);
        if (next && (vma != next) && (end == next->vm_end)) {
                int ret;

                remove_next = true;
                vma_start_write(next);
                ret = dup_anon_vma(vma, next, &anon_dup);
                if (ret)
                        return ret;
        }

        init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
        /* Not merging but overwriting any part of next is not handled. */
        VM_WARN_ON(next && !vp.remove &&
                  next != vma && end > next->vm_start);
        /* Only handles expanding */
        VM_WARN_ON(vma->vm_start < start || vma->vm_end > end);

        /* Note: vma iterator must be pointing to 'start' */
        vma_iter_config(vmi, start, end);
        if (vma_iter_prealloc(vmi, vma))
                goto nomem;

        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, start, end, 0);
        vma_set_range(vma, start, end, pgoff);
        vma_iter_store(vmi, vma);

        vma_complete(&vp, vmi, vma->vm_mm);
        return 0;

nomem:
        if (anon_dup)
                unlink_anon_vmas(anon_dup);
        return -ENOMEM;
}

/*
 * vma_shrink() - Reduce an existing VMAs memory area
 * @vmi: The vma iterator
 * @vma: The VMA to modify
 * @start: The new start
 * @end: The new end
 *
 * Returns: 0 on success, -ENOMEM otherwise
 */
int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
               unsigned long start, unsigned long end, pgoff_t pgoff)
{
        struct vma_prepare vp;

        WARN_ON((vma->vm_start != start) && (vma->vm_end != end));

        if (vma->vm_start < start)
                vma_iter_config(vmi, vma->vm_start, start);
        else
                vma_iter_config(vmi, end, vma->vm_end);

        if (vma_iter_prealloc(vmi, NULL))
                return -ENOMEM;

        vma_start_write(vma);

        init_vma_prep(&vp, vma);
        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, start, end, 0);

        vma_iter_clear(vmi);
        vma_set_range(vma, start, end, pgoff);
        vma_complete(&vp, vmi, vma->vm_mm);
        return 0;
}

/*
 * If the vma has a ->close operation then the driver probably needs to release
 * per-vma resources, so we don't attempt to merge those if the caller indicates
 * the current vma may be removed as part of the merge.
 */
static inline bool is_mergeable_vma(struct vm_area_struct *vma,
                struct file *file, unsigned long vm_flags,
                struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name, bool may_remove_vma)
{
        /*
         * VM_SOFTDIRTY should not prevent from VMA merging, if we
         * match the flags but dirty bit -- the caller should mark
         * merged VMA as dirty. If dirty bit won't be excluded from
         * comparison, we increase pressure on the memory system forcing
         * the kernel to generate new VMAs when old one could be
         * extended instead.
         */
        if ((vma->vm_flags ^ vm_flags) & ~VM_SOFTDIRTY)
                return false;
        if (vma->vm_file != file)
                return false;
        if (may_remove_vma && vma->vm_ops && vma->vm_ops->close)
                return false;
        if (!is_mergeable_vm_userfaultfd_ctx(vma, vm_userfaultfd_ctx))
                return false;
        if (!anon_vma_name_eq(anon_vma_name(vma), anon_name))
                return false;
        return true;
}

static inline bool is_mergeable_anon_vma(struct anon_vma *anon_vma1,
                 struct anon_vma *anon_vma2, struct vm_area_struct *vma)
{
        /*
         * The list_is_singular() test is to avoid merging VMA cloned from
         * parents. This can improve scalability caused by anon_vma lock.
         */
        if ((!anon_vma1 || !anon_vma2) && (!vma ||
                list_is_singular(&vma->anon_vma_chain)))
                return true;
        return anon_vma1 == anon_vma2;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * in front of (at a lower virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 *
 * We don't check here for the merged mmap wrapping around the end of pagecache
 * indices (16TB on ia32) because do_mmap() does not permit mmap's which
 * wrap, nor mmaps which cover the final page at index -1UL.
 *
 * We assume the vma may be removed as part of the merge.
 */
static bool
can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
                struct anon_vma *anon_vma, struct file *file,
                pgoff_t vm_pgoff, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, true) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                if (vma->vm_pgoff == vm_pgoff)
                        return true;
        }
        return false;
}

/*
 * Return true if we can merge this (vm_flags,anon_vma,file,vm_pgoff)
 * beyond (at a higher virtual address and file offset than) the vma.
 *
 * We cannot merge two vmas if they have differently assigned (non-NULL)
 * anon_vmas, nor if same anon_vma is assigned but offsets incompatible.
 *
 * We assume that vma is not removed as part of the merge.
 */
static bool
can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
                struct anon_vma *anon_vma, struct file *file,
                pgoff_t vm_pgoff, struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
                struct anon_vma_name *anon_name)
{
        if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name, false) &&
            is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
                pgoff_t vm_pglen;
                vm_pglen = vma_pages(vma);
                if (vma->vm_pgoff + vm_pglen == vm_pgoff)
                        return true;
        }
        return false;
}

/*
 * Given a mapping request (addr,end,vm_flags,file,pgoff,anon_name),
 * figure out whether that can be merged with its predecessor or its
 * successor.  Or both (it neatly fills a hole).
 *
 * In most cases - when called for mmap, brk or mremap - [addr,end) is
 * certain not to be mapped by the time vma_merge is called; but when
 * called for mprotect, it is certain to be already mapped (either at
 * an offset within prev, or at the start of next), and the flags of
 * this area are about to be changed to vm_flags - and the no-change
 * case has already been eliminated.
 *
 * The following mprotect cases have to be considered, where **** is
 * the area passed down from mprotect_fixup, never extending beyond one
 * vma, PPPP is the previous vma, CCCC is a concurrent vma that starts
 * at the same address as **** and is of the same or larger span, and
 * NNNN the next vma after ****:
 *
 *     ****             ****                   ****
 *    PPPPPPNNNNNN    PPPPPPNNNNNN       PPPPPPCCCCCC
 *    cannot merge    might become       might become
 *                    PPNNNNNNNNNN       PPPPPPPPPPCC
 *    mmap, brk or    case 4 below       case 5 below
 *    mremap move:
 *                        ****               ****
 *                    PPPP    NNNN       PPPPCCCCNNNN
 *                    might become       might become
 *                    PPPPPPPPPPPP 1 or  PPPPPPPPPPPP 6 or
 *                    PPPPPPPPNNNN 2 or  PPPPPPPPNNNN 7 or
 *                    PPPPNNNNNNNN 3     PPPPNNNNNNNN 8
 *
 * It is important for case 8 that the vma CCCC overlapping the
 * region **** is never going to extended over NNNN. Instead NNNN must
 * be extended in region **** and CCCC must be removed. This way in
 * all cases where vma_merge succeeds, the moment vma_merge drops the
 * rmap_locks, the properties of the merged vma will be already
 * correct for the whole merged range. Some of those properties like
 * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
 * be correct for the whole merged range immediately after the
 * rmap_locks are released. Otherwise if NNNN would be removed and
 * CCCC would be extended over the NNNN range, remove_migration_ptes
 * or other rmap walkers (if working on addresses beyond the "end"
 * parameter) may establish ptes with the wrong permissions of CCCC
 * instead of the right permissions of NNNN.
 *
 * In the code below:
 * PPPP is represented by *prev
 * CCCC is represented by *curr or not represented at all (NULL)
 * NNNN is represented by *next or not represented at all (NULL)
 * **** is not represented - it will be merged and the vma containing the
 *      area is returned, or the function will return NULL
 */
static struct vm_area_struct
*vma_merge(struct vma_iterator *vmi, struct vm_area_struct *prev,
           struct vm_area_struct *src, unsigned long addr, unsigned long end,
           unsigned long vm_flags, pgoff_t pgoff, struct mempolicy *policy,
           struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
           struct anon_vma_name *anon_name)
{
        struct mm_struct *mm = src->vm_mm;
        struct anon_vma *anon_vma = src->anon_vma;
        struct file *file = src->vm_file;
        struct vm_area_struct *curr, *next, *res;
        struct vm_area_struct *vma, *adjust, *remove, *remove2;
        struct vm_area_struct *anon_dup = NULL;
        struct vma_prepare vp;
        pgoff_t vma_pgoff;
        int err = 0;
        bool merge_prev = false;
        bool merge_next = false;
        bool vma_expanded = false;
        unsigned long vma_start = addr;
        unsigned long vma_end = end;
        pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
        long adj_start = 0;

        /*
         * We later require that vma->vm_flags == vm_flags,
         * so this tests vma->vm_flags & VM_SPECIAL, too.
         */
        if (vm_flags & VM_SPECIAL)
                return NULL;

        /* Does the input range span an existing VMA? (cases 5 - 8) */
        curr = find_vma_intersection(mm, prev ? prev->vm_end : 0, end);

        if (!curr ||                    /* cases 1 - 4 */
            end == curr->vm_end)        /* cases 6 - 8, adjacent VMA */
                next = vma_lookup(mm, end);
        else
                next = NULL;            /* case 5 */

        if (prev) {
                vma_start = prev->vm_start;
                vma_pgoff = prev->vm_pgoff;

                /* Can we merge the predecessor? */
                if (addr == prev->vm_end && mpol_equal(vma_policy(prev), policy)
                    && can_vma_merge_after(prev, vm_flags, anon_vma, file,
                                           pgoff, vm_userfaultfd_ctx, anon_name)) {
                        merge_prev = true;
                        vma_prev(vmi);
                }
        }

        /* Can we merge the successor? */
        if (next && mpol_equal(policy, vma_policy(next)) &&
            can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen,
                                 vm_userfaultfd_ctx, anon_name)) {
                merge_next = true;
        }

        /* Verify some invariant that must be enforced by the caller. */
        VM_WARN_ON(prev && addr <= prev->vm_start);
        VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
        VM_WARN_ON(addr >= end);

        if (!merge_prev && !merge_next)
                return NULL; /* Not mergeable. */

        if (merge_prev)
                vma_start_write(prev);

        res = vma = prev;
        remove = remove2 = adjust = NULL;

        /* Can we merge both the predecessor and the successor? */
        if (merge_prev && merge_next &&
            is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
                vma_start_write(next);
                remove = next;                          /* case 1 */
                vma_end = next->vm_end;
                err = dup_anon_vma(prev, next, &anon_dup);
                if (curr) {                             /* case 6 */
                        vma_start_write(curr);
                        remove = curr;
                        remove2 = next;
                        /*
                         * Note that the dup_anon_vma below cannot overwrite err
                         * since the first caller would do nothing unless next
                         * has an anon_vma.
                         */
                        if (!next->anon_vma)
                                err = dup_anon_vma(prev, curr, &anon_dup);
                }
        } else if (merge_prev) {                        /* case 2 */
                if (curr) {
                        vma_start_write(curr);
                        if (end == curr->vm_end) {      /* case 7 */
                                /*
                                 * can_vma_merge_after() assumed we would not be
                                 * removing prev vma, so it skipped the check
                                 * for vm_ops->close, but we are removing curr
                                 */
                                if (curr->vm_ops && curr->vm_ops->close)
                                        err = -EINVAL;
                                remove = curr;
                        } else {                        /* case 5 */
                                adjust = curr;
                                adj_start = (end - curr->vm_start);
                        }
                        if (!err)
                                err = dup_anon_vma(prev, curr, &anon_dup);
                }
        } else { /* merge_next */
                vma_start_write(next);
                res = next;
                if (prev && addr < prev->vm_end) {      /* case 4 */
                        vma_start_write(prev);
                        vma_end = addr;
                        adjust = next;
                        adj_start = -(prev->vm_end - addr);
                        err = dup_anon_vma(next, prev, &anon_dup);
                } else {
                        /*
                         * Note that cases 3 and 8 are the ONLY ones where prev
                         * is permitted to be (but is not necessarily) NULL.
                         */
                        vma = next;                     /* case 3 */
                        vma_start = addr;
                        vma_end = next->vm_end;
                        vma_pgoff = next->vm_pgoff - pglen;
                        if (curr) {                     /* case 8 */
                                vma_pgoff = curr->vm_pgoff;
                                vma_start_write(curr);
                                remove = curr;
                                err = dup_anon_vma(next, curr, &anon_dup);
                        }
                }
        }

        /* Error in anon_vma clone. */
        if (err)
                goto anon_vma_fail;

        if (vma_start < vma->vm_start || vma_end > vma->vm_end)
                vma_expanded = true;

        if (vma_expanded) {
                vma_iter_config(vmi, vma_start, vma_end);
        } else {
                vma_iter_config(vmi, adjust->vm_start + adj_start,
                                adjust->vm_end);
        }

        if (vma_iter_prealloc(vmi, vma))
                goto prealloc_fail;

        init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
        VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
                   vp.anon_vma != adjust->anon_vma);

        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, vma_start, vma_end, adj_start);
        vma_set_range(vma, vma_start, vma_end, vma_pgoff);

        if (vma_expanded)
                vma_iter_store(vmi, vma);

        if (adj_start) {
                adjust->vm_start += adj_start;
                adjust->vm_pgoff += adj_start >> PAGE_SHIFT;
                if (adj_start < 0) {
                        WARN_ON(vma_expanded);
                        vma_iter_store(vmi, next);
                }
        }

        vma_complete(&vp, vmi, mm);
        khugepaged_enter_vma(res, vm_flags);
        return res;

prealloc_fail:
        if (anon_dup)
                unlink_anon_vmas(anon_dup);

anon_vma_fail:
        vma_iter_set(vmi, addr);
        vma_iter_load(vmi);
        return NULL;
}

/*
 * Rough compatibility check to quickly see if it's even worth looking
 * at sharing an anon_vma.
 *
 * They need to have the same vm_file, and the flags can only differ
 * in things that mprotect may change.
 *
 * NOTE! The fact that we share an anon_vma doesn't _have_ to mean that
 * we can merge the two vma's. For example, we refuse to merge a vma if
 * there is a vm_ops->close() function, because that indicates that the
 * driver is doing some kind of reference counting. But that doesn't
 * really matter for the anon_vma sharing case.
 */
static int anon_vma_compatible(struct vm_area_struct *a, struct vm_area_struct *b)
{
        return a->vm_end == b->vm_start &&
                mpol_equal(vma_policy(a), vma_policy(b)) &&
                a->vm_file == b->vm_file &&
                !((a->vm_flags ^ b->vm_flags) & ~(VM_ACCESS_FLAGS | VM_SOFTDIRTY)) &&
                b->vm_pgoff == a->vm_pgoff + ((b->vm_start - a->vm_start) >> PAGE_SHIFT);
}

/*
 * Do some basic sanity checking to see if we can re-use the anon_vma
 * from 'old'. The 'a'/'b' vma's are in VM order - one of them will be
 * the same as 'old', the other will be the new one that is trying
 * to share the anon_vma.
 *
 * NOTE! This runs with mmap_lock held for reading, so it is possible that
 * the anon_vma of 'old' is concurrently in the process of being set up
 * by another page fault trying to merge _that_. But that's ok: if it
 * is being set up, that automatically means that it will be a singleton
 * acceptable for merging, so we can do all of this optimistically. But
 * we do that READ_ONCE() to make sure that we never re-load the pointer.
 *
 * IOW: that the "list_is_singular()" test on the anon_vma_chain only
 * matters for the 'stable anon_vma' case (ie the thing we want to avoid
 * is to return an anon_vma that is "complex" due to having gone through
 * a fork).
 *
 * We also make sure that the two vma's are compatible (adjacent,
 * and with the same memory policies). That's all stable, even with just
 * a read lock on the mmap_lock.
 */
static struct anon_vma *reusable_anon_vma(struct vm_area_struct *old, struct vm_area_struct *a, struct vm_area_struct *b)
{
        if (anon_vma_compatible(a, b)) {
                struct anon_vma *anon_vma = READ_ONCE(old->anon_vma);

                if (anon_vma && list_is_singular(&old->anon_vma_chain))
                        return anon_vma;
        }
        return NULL;
}

/*
 * find_mergeable_anon_vma is used by anon_vma_prepare, to check
 * neighbouring vmas for a suitable anon_vma, before it goes off
 * to allocate a new anon_vma.  It checks because a repetitive
 * sequence of mprotects and faults may otherwise lead to distinct
 * anon_vmas being allocated, preventing vma merge in subsequent
 * mprotect.
 */
struct anon_vma *find_mergeable_anon_vma(struct vm_area_struct *vma)
{
        struct anon_vma *anon_vma = NULL;
        struct vm_area_struct *prev, *next;
        VMA_ITERATOR(vmi, vma->vm_mm, vma->vm_end);

        /* Try next first. */
        next = vma_iter_load(&vmi);
        if (next) {
                anon_vma = reusable_anon_vma(next, vma, next);
                if (anon_vma)
                        return anon_vma;
        }

        prev = vma_prev(&vmi);
        VM_BUG_ON_VMA(prev != vma, vma);
        prev = vma_prev(&vmi);
        /* Try prev next. */
        if (prev)
                anon_vma = reusable_anon_vma(prev, prev, vma);

        /*
         * We might reach here with anon_vma == NULL if we can't find
         * any reusable anon_vma.
         * There's no absolute need to look only at touching neighbours:
         * we could search further afield for "compatible" anon_vmas.
         * But it would probably just be a waste of time searching,
         * or lead to too many vmas hanging off the same anon_vma.
         * We're trying to allow mprotect remerging later on,
         * not trying to minimize memory used for anon_vmas.
         */
        return anon_vma;
}

/*
 * If a hint addr is less than mmap_min_addr change hint to be as
 * low as possible but still greater than mmap_min_addr
 */
static inline unsigned long round_hint_to_min(unsigned long hint)
{
        hint &= PAGE_MASK;
        if (((void *)hint != NULL) &&
            (hint < mmap_min_addr))
                return PAGE_ALIGN(mmap_min_addr);
        return hint;
}

bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
                        unsigned long bytes)
{
        unsigned long locked_pages, limit_pages;

        if (!(flags & VM_LOCKED) || capable(CAP_IPC_LOCK))
                return true;

        locked_pages = bytes >> PAGE_SHIFT;
        locked_pages += mm->locked_vm;

        limit_pages = rlimit(RLIMIT_MEMLOCK);
        limit_pages >>= PAGE_SHIFT;

        return locked_pages <= limit_pages;
}

static inline u64 file_mmap_size_max(struct file *file, struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISBLK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISSOCK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        /* Special "we do even unsigned file positions" case */
        if (file->f_mode & FMODE_UNSIGNED_OFFSET)
                return 0;

        /* Yes, random drivers might want more. But I'm tired of buggy drivers */
        return ULONG_MAX;
}

static inline bool file_mmap_ok(struct file *file, struct inode *inode,
                                unsigned long pgoff, unsigned long len)
{
        u64 maxsize = file_mmap_size_max(file, inode);

        if (maxsize && len > maxsize)
                return false;
        maxsize -= len;
        if (pgoff > maxsize >> PAGE_SHIFT)
                return false;
        return true;
}

/*
 * The caller must write-lock current->mm->mmap_lock.
 */
unsigned long do_mmap(struct file *file, unsigned long addr,
                        unsigned long len, unsigned long prot,
                        unsigned long flags, vm_flags_t vm_flags,
                        unsigned long pgoff, unsigned long *populate,
                        struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        int pkey = 0;

        *populate = 0;

        if (!len)
                return -EINVAL;

        /*
         * Does the application expect PROT_READ to imply PROT_EXEC?
         *
         * (the exception is when the underlying filesystem is noexec
         *  mounted, in which case we don't add PROT_EXEC.)
         */
        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                if (!(file && path_noexec(&file->f_path)))
                        prot |= PROT_EXEC;

        /* force arch specific MAP_FIXED handling in get_unmapped_area */
        if (flags & MAP_FIXED_NOREPLACE)
                flags |= MAP_FIXED;

        if (!(flags & MAP_FIXED))
                addr = round_hint_to_min(addr);

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len)
                return -ENOMEM;

        /* offset overflow? */
        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                return -EOVERFLOW;

        /* Too many mappings? */
        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        if (prot == PROT_EXEC) {
                pkey = execute_only_pkey(mm);
                if (pkey < 0)
                        pkey = 0;
        }

        /* Do simple checking here so the lower-level routines won't have
         * to. we assume access permissions have been handled by the open
         * of the memory object, so we don't do any here.
         */
        vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
                        mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        addr = __get_unmapped_area(file, addr, len, pgoff, flags, vm_flags);
        if (IS_ERR_VALUE(addr))
                return addr;

        if (flags & MAP_FIXED_NOREPLACE) {
                if (find_vma_intersection(mm, addr, addr + len))
                        return -EEXIST;
        }

        if (flags & MAP_LOCKED)
                if (!can_do_mlock())
                        return -EPERM;

        if (!mlock_future_ok(mm, vm_flags, len))
                return -EAGAIN;

        if (file) {
                struct inode *inode = file_inode(file);
                unsigned long flags_mask;

                if (!file_mmap_ok(file, inode, pgoff, len))
                        return -EOVERFLOW;

                flags_mask = LEGACY_MAP_MASK;
                if (file->f_op->fop_flags & FOP_MMAP_SYNC)
                        flags_mask |= MAP_SYNC;

                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        /*
                         * Force use of MAP_SHARED_VALIDATE with non-legacy
                         * flags. E.g. MAP_SYNC is dangerous to use with
                         * MAP_SHARED as you don't know which consistency model
                         * you will get. We silently ignore unsupported flags
                         * with MAP_SHARED to preserve backward compatibility.
                         */
                        flags &= LEGACY_MAP_MASK;
                        fallthrough;
                case MAP_SHARED_VALIDATE:
                        if (flags & ~flags_mask)
                                return -EOPNOTSUPP;
                        if (prot & PROT_WRITE) {
                                if (!(file->f_mode & FMODE_WRITE))
                                        return -EACCES;
                                if (IS_SWAPFILE(file->f_mapping->host))
                                        return -ETXTBSY;
                        }

                        /*
                         * Make sure we don't allow writing to an append-only
                         * file..
                         */
                        if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        if (!(file->f_mode & FMODE_WRITE))
                                vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
                        fallthrough;
                case MAP_PRIVATE:
                        if (!(file->f_mode & FMODE_READ))
                                return -EACCES;
                        if (path_noexec(&file->f_path)) {
                                if (vm_flags & VM_EXEC)
                                        return -EPERM;
                                vm_flags &= ~VM_MAYEXEC;
                        }

                        if (!file->f_op->mmap)
                                return -ENODEV;
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        break;

                default:
                        return -EINVAL;
                }
        } else {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        /*
                         * Ignore pgoff.
                         */
                        pgoff = 0;
                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        break;
                case MAP_PRIVATE:
                        /*
                         * Set pgoff according to addr for anon_vma.
                         */
                        pgoff = addr >> PAGE_SHIFT;
                        break;
                default:
                        return -EINVAL;
                }
        }

        /*
         * Set 'VM_NORESERVE' if we should not account for the
         * memory use of this mapping.
         */
        if (flags & MAP_NORESERVE) {
                /* We honor MAP_NORESERVE if allowed to overcommit */
                if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
                        vm_flags |= VM_NORESERVE;

                /* hugetlb applies strict overcommit unless MAP_NORESERVE */
                if (file && is_file_hugepages(file))
                        vm_flags |= VM_NORESERVE;
        }

        addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
        if (!IS_ERR_VALUE(addr) &&
            ((vm_flags & VM_LOCKED) ||
             (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
                *populate = len;
        return addr;
}

unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
                              unsigned long prot, unsigned long flags,
                              unsigned long fd, unsigned long pgoff)
{
        struct file *file = NULL;
        unsigned long retval;

        if (!(flags & MAP_ANONYMOUS)) {
                audit_mmap_fd(fd, flags);
                file = fget(fd);
                if (!file)
                        return -EBADF;
                if (is_file_hugepages(file)) {
                        len = ALIGN(len, huge_page_size(hstate_file(file)));
                } else if (unlikely(flags & MAP_HUGETLB)) {
                        retval = -EINVAL;
                        goto out_fput;
                }
        } else if (flags & MAP_HUGETLB) {
                struct hstate *hs;

                hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (!hs)
                        return -EINVAL;

                len = ALIGN(len, huge_page_size(hs));
                /*
                 * VM_NORESERVE is used because the reservations will be
                 * taken when vm_ops->mmap() is called
                 */
                file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
                                VM_NORESERVE,
                                HUGETLB_ANONHUGE_INODE,
                                (flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (IS_ERR(file))
                        return PTR_ERR(file);
        }

        retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
out_fput:
        if (file)
                fput(file);
        return retval;
}

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
                unsigned long, prot, unsigned long, flags,
                unsigned long, fd, unsigned long, pgoff)
{
        return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
}

#ifdef __ARCH_WANT_SYS_OLD_MMAP
struct mmap_arg_struct {
        unsigned long addr;
        unsigned long len;
        unsigned long prot;
        unsigned long flags;
        unsigned long fd;
        unsigned long offset;
};

SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
{
        struct mmap_arg_struct a;

        if (copy_from_user(&a, arg, sizeof(a)))
                return -EFAULT;
        if (offset_in_page(a.offset))
                return -EINVAL;

        return ksys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                               a.offset >> PAGE_SHIFT);
}
#endif /* __ARCH_WANT_SYS_OLD_MMAP */

static bool vm_ops_needs_writenotify(const struct vm_operations_struct *vm_ops)
{
        return vm_ops && (vm_ops->page_mkwrite || vm_ops->pfn_mkwrite);
}

static bool vma_is_shared_writable(struct vm_area_struct *vma)
{
        return (vma->vm_flags & (VM_WRITE | VM_SHARED)) ==
                (VM_WRITE | VM_SHARED);
}

static bool vma_fs_can_writeback(struct vm_area_struct *vma)
{
        /* No managed pages to writeback. */
        if (vma->vm_flags & VM_PFNMAP)
                return false;

        return vma->vm_file && vma->vm_file->f_mapping &&
                mapping_can_writeback(vma->vm_file->f_mapping);
}

/*
 * Does this VMA require the underlying folios to have their dirty state
 * tracked?
 */
bool vma_needs_dirty_tracking(struct vm_area_struct *vma)
{
        /* Only shared, writable VMAs require dirty tracking. */
        if (!vma_is_shared_writable(vma))
                return false;

        /* Does the filesystem need to be notified? */
        if (vm_ops_needs_writenotify(vma->vm_ops))
                return true;

        /*
         * Even if the filesystem doesn't indicate a need for writenotify, if it
         * can writeback, dirty tracking is still required.
         */
        return vma_fs_can_writeback(vma);
}

/*
 * Some shared mappings will want the pages marked read-only
 * to track write events. If so, we'll downgrade vm_page_prot
 * to the private version (using protection_map[] without the
 * VM_SHARED bit).
 */
bool vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
{
        /* If it was private or non-writable, the write bit is already clear */
        if (!vma_is_shared_writable(vma))
                return false;

        /* The backer wishes to know when pages are first written to? */
        if (vm_ops_needs_writenotify(vma->vm_ops))
                return true;

        /* The open routine did something to the protections that pgprot_modify
         * won't preserve? */
        if (pgprot_val(vm_page_prot) !=
            pgprot_val(vm_pgprot_modify(vm_page_prot, vma->vm_flags)))
                return false;

        /*
         * Do we need to track softdirty? hugetlb does not support softdirty
         * tracking yet.
         */
        if (vma_soft_dirty_enabled(vma) && !is_vm_hugetlb_page(vma))
                return true;

        /* Do we need write faults for uffd-wp tracking? */
        if (userfaultfd_wp(vma))
                return true;

        /* Can the mapping track the dirty pages? */
        return vma_fs_can_writeback(vma);
}

/*
 * We account for memory if it's a private writeable mapping,
 * not hugepages and VM_NORESERVE wasn't set.
 */
static inline bool accountable_mapping(struct file *file, vm_flags_t vm_flags)
{
        /*
         * hugetlb has its own accounting separate from the core VM
         * VM_HUGETLB may not be set yet so we cannot check for that flag.
         */
        if (file && is_file_hugepages(file))
                return false;

        return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}

/**
 * unmapped_area() - Find an area between the low_limit and the high_limit with
 * the correct alignment and offset, all from @info. Note: current->mm is used
 * for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_lowest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        /*
         * Adjust for the gap first so it doesn't interfere with the
         * later alignment. The first step is the minimum needed to
         * fulill the start gap, the next steps is the minimum to align
         * that. It is the minimum needed to fulill both.
         */
        gap = vma_iter_addr(&vmi) + info->start_gap;
        gap += (info->align_offset - gap) & info->align_mask;
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap + length - 1) {
                        low_limit = tmp->vm_end;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        low_limit = vm_end_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/**
 * unmapped_area_topdown() - Find an area between the low_limit and the
 * high_limit with the correct alignment and offset at the highest available
 * address, all from @info. Note: current->mm is used for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap, gap_end;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_highest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        gap = vma_iter_end(&vmi) - info->length;
        gap -= (gap - info->align_offset) & info->align_mask;
        gap_end = vma_iter_end(&vmi);
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap_end) {
                        high_limit = vm_start_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        high_limit = tmp->vm_start;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/*
 * Search for an unmapped address range.
 *
 * We are looking for a range that:
 * - does not intersect with any VMA;
 * - is contained within the [low_limit, high_limit) interval;
 * - is at least the desired size.
 * - satisfies (begin_addr & align_mask) == (align_offset & align_mask)
 */
unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long addr;

        if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
                addr = unmapped_area_topdown(info);
        else
                addr = unmapped_area(info);

        trace_vm_unmapped_area(addr, info);
        return addr;
}

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *      if (ret & ~PAGE_MASK)
 *              error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
unsigned long
generic_get_unmapped_area(struct file *filp, unsigned long addr,
                          unsigned long len, unsigned long pgoff,
                          unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev;
        struct vm_unmapped_area_info info = {};
        const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);

        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                    (!vma || addr + len <= vm_start_gap(vma)) &&
                    (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.length = len;
        info.low_limit = mm->mmap_base;
        info.high_limit = mmap_end;
        return vm_unmapped_area(&info);
}

#ifndef HAVE_ARCH_UNMAPPED_AREA
unsigned long
arch_get_unmapped_area(struct file *filp, unsigned long addr,
                       unsigned long len, unsigned long pgoff,
                       unsigned long flags)
{
        return generic_get_unmapped_area(filp, addr, len, pgoff, flags);
}
#endif

/*
 * This mmap-allocator allocates new areas top-down from below the
 * stack's low limit (the base):
 */
unsigned long
generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
                                  unsigned long len, unsigned long pgoff,
                                  unsigned long flags)
{
        struct vm_area_struct *vma, *prev;
        struct mm_struct *mm = current->mm;
        struct vm_unmapped_area_info info = {};
        const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);

        /* requested length too big for entire address space */
        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        /* requesting a specific address */
        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                                (!vma || addr + len <= vm_start_gap(vma)) &&
                                (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.flags = VM_UNMAPPED_AREA_TOPDOWN;
        info.length = len;
        info.low_limit = PAGE_SIZE;
        info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
        addr = vm_unmapped_area(&info);

        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        if (offset_in_page(addr)) {
                VM_BUG_ON(addr != -ENOMEM);
                info.flags = 0;
                info.low_limit = TASK_UNMAPPED_BASE;
                info.high_limit = mmap_end;
                addr = vm_unmapped_area(&info);
        }

        return addr;
}

#ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
                               unsigned long len, unsigned long pgoff,
                               unsigned long flags)
{
        return generic_get_unmapped_area_topdown(filp, addr, len, pgoff, flags);
}
#endif

#ifndef HAVE_ARCH_UNMAPPED_AREA_VMFLAGS
unsigned long
arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned long len,
                               unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
{
        return arch_get_unmapped_area(filp, addr, len, pgoff, flags);
}

unsigned long
arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr,
                                       unsigned long len, unsigned long pgoff,
                                       unsigned long flags, vm_flags_t vm_flags)
{
        return arch_get_unmapped_area_topdown(filp, addr, len, pgoff, flags);
}
#endif

unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm, struct file *filp,
                                           unsigned long addr, unsigned long len,
                                           unsigned long pgoff, unsigned long flags,
                                           vm_flags_t vm_flags)
{
        if (test_bit(MMF_TOPDOWN, &mm->flags))
                return arch_get_unmapped_area_topdown_vmflags(filp, addr, len, pgoff,
                                                              flags, vm_flags);
        return arch_get_unmapped_area_vmflags(filp, addr, len, pgoff, flags, vm_flags);
}

unsigned long
__get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
                unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
{
        unsigned long (*get_area)(struct file *, unsigned long,
                                  unsigned long, unsigned long, unsigned long)
                                  = NULL;

        unsigned long error = arch_mmap_check(addr, len, flags);
        if (error)
                return error;

        /* Careful about overflows.. */
        if (len > TASK_SIZE)
                return -ENOMEM;

        if (file) {
                if (file->f_op->get_unmapped_area)
                        get_area = file->f_op->get_unmapped_area;
        } else if (flags & MAP_SHARED) {
                /*
                 * mmap_region() will call shmem_zero_setup() to create a file,
                 * so use shmem's get_unmapped_area in case it can be huge.
                 */
                get_area = shmem_get_unmapped_area;
        }

        /* Always treat pgoff as zero for anonymous memory. */
        if (!file)
                pgoff = 0;

        if (get_area) {
                addr = get_area(file, addr, len, pgoff, flags);
        } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
                /* Ensures that larger anonymous mappings are THP aligned. */
                addr = thp_get_unmapped_area_vmflags(file, addr, len,
                                                     pgoff, flags, vm_flags);
        } else {
                addr = mm_get_unmapped_area_vmflags(current->mm, file, addr, len,
                                                    pgoff, flags, vm_flags);
        }
        if (IS_ERR_VALUE(addr))
                return addr;

        if (addr > TASK_SIZE - len)
                return -ENOMEM;
        if (offset_in_page(addr))
                return -EINVAL;

        error = security_mmap_addr(addr);
        return error ? error : addr;
}

unsigned long
mm_get_unmapped_area(struct mm_struct *mm, struct file *file,
                     unsigned long addr, unsigned long len,
                     unsigned long pgoff, unsigned long flags)
{
        if (test_bit(MMF_TOPDOWN, &mm->flags))
                return arch_get_unmapped_area_topdown(file, addr, len, pgoff, flags);
        return arch_get_unmapped_area(file, addr, len, pgoff, flags);
}
EXPORT_SYMBOL(mm_get_unmapped_area);

/**
 * find_vma_intersection() - Look up the first VMA which intersects the interval
 * @mm: The process address space.
 * @start_addr: The inclusive start user address.
 * @end_addr: The exclusive end user address.
 *
 * Returns: The first VMA within the provided range, %NULL otherwise.  Assumes
 * start_addr < end_addr.
 */
struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
                                             unsigned long start_addr,
                                             unsigned long end_addr)
{
        unsigned long index = start_addr;

        mmap_assert_locked(mm);
        return mt_find(&mm->mm_mt, &index, end_addr - 1);
}
EXPORT_SYMBOL(find_vma_intersection);

/**
 * find_vma() - Find the VMA for a given address, or the next VMA.
 * @mm: The mm_struct to check
 * @addr: The address
 *
 * Returns: The VMA associated with addr, or the next VMA.
 * May return %NULL in the case of no VMA at addr or above.
 */
struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
{
        unsigned long index = addr;

        mmap_assert_locked(mm);
        return mt_find(&mm->mm_mt, &index, ULONG_MAX);
}
EXPORT_SYMBOL(find_vma);

/**
 * find_vma_prev() - Find the VMA for a given address, or the next vma and
 * set %pprev to the previous VMA, if any.
 * @mm: The mm_struct to check
 * @addr: The address
 * @pprev: The pointer to set to the previous VMA
 *
 * Note that RCU lock is missing here since the external mmap_lock() is used
 * instead.
 *
 * Returns: The VMA associated with @addr, or the next vma.
 * May return %NULL in the case of no vma at addr or above.
 */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
                        struct vm_area_struct **pprev)
{
        struct vm_area_struct *vma;
        VMA_ITERATOR(vmi, mm, addr);

        vma = vma_iter_load(&vmi);
        *pprev = vma_prev(&vmi);
        if (!vma)
                vma = vma_next(&vmi);
        return vma;
}

/*
 * Verify that the stack growth is acceptable and
 * update accounting. This is shared with both the
 * grow-up and grow-down cases.
 */
static int acct_stack_growth(struct vm_area_struct *vma,
                             unsigned long size, unsigned long grow)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long new_start;

        /* address space limit tests */
        if (!may_expand_vm(mm, vma->vm_flags, grow))
                return -ENOMEM;

        /* Stack limit test */
        if (size > rlimit(RLIMIT_STACK))
                return -ENOMEM;

        /* mlock limit tests */
        if (!mlock_future_ok(mm, vma->vm_flags, grow << PAGE_SHIFT))
                return -ENOMEM;

        /* Check to ensure the stack will not grow into a hugetlb-only region */
        new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
                        vma->vm_end - size;
        if (is_hugepage_only_range(vma->vm_mm, new_start, size))
                return -EFAULT;

        /*
         * Overcommit..  This must be the final test, as it will
         * update security statistics.
         */
        if (security_vm_enough_memory_mm(mm, grow))
                return -ENOMEM;

        return 0;
}

#if defined(CONFIG_STACK_GROWSUP)
/*
 * PA-RISC uses this for its stack.
 * vma is the last one with address > vma->vm_end.  Have to extend vma.
 */
static int expand_upwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next;
        unsigned long gap_addr;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

        if (!(vma->vm_flags & VM_GROWSUP))
                return -EFAULT;

        /* Guard against exceeding limits of the address space. */
        address &= PAGE_MASK;
        if (address >= (TASK_SIZE & PAGE_MASK))
                return -ENOMEM;
        address += PAGE_SIZE;

        /* Enforce stack_guard_gap */
        gap_addr = address + stack_guard_gap;

        /* Guard against overflow */
        if (gap_addr < address || gap_addr > TASK_SIZE)
                gap_addr = TASK_SIZE;

        next = find_vma_intersection(mm, vma->vm_end, gap_addr);
        if (next && vma_is_accessible(next)) {
                if (!(next->vm_flags & VM_GROWSUP))
                        return -ENOMEM;
                /* Check that both stack segments have the same anon_vma? */
        }

        if (next)
                vma_iter_prev_range_limit(&vmi, address);

        vma_iter_config(&vmi, vma->vm_start, address);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address > vma->vm_end) {
                unsigned long size, grow;

                size = address - vma->vm_start;
                grow = (address - vma->vm_end) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * We only hold a shared mmap_lock lock here, so
                                 * we need to protect against concurrent vma
                                 * expansions.  anon_vma_lock_write() doesn't
                                 * help here, as we don't guarantee that all
                                 * growable vmas in a mm share the same root
                                 * anon vma.  So, we reuse mm->page_table_lock
                                 * to guard against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_end = address;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}
#endif /* CONFIG_STACK_GROWSUP */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 * mmap_lock held for writing.
 */
int expand_downwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *prev;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

        if (!(vma->vm_flags & VM_GROWSDOWN))
                return -EFAULT;

        address &= PAGE_MASK;
        if (address < mmap_min_addr || address < FIRST_USER_ADDRESS)
                return -EPERM;

        /* Enforce stack_guard_gap */
        prev = vma_prev(&vmi);
        /* Check that both stack segments have the same anon_vma? */
        if (prev) {
                if (!(prev->vm_flags & VM_GROWSDOWN) &&
                    vma_is_accessible(prev) &&
                    (address - prev->vm_end < stack_guard_gap))
                        return -ENOMEM;
        }

        if (prev)
                vma_iter_next_range_limit(&vmi, vma->vm_start);

        vma_iter_config(&vmi, address, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address < vma->vm_start) {
                unsigned long size, grow;

                size = vma->vm_end - address;
                grow = (vma->vm_start - address) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (grow <= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * We only hold a shared mmap_lock lock here, so
                                 * we need to protect against concurrent vma
                                 * expansions.  anon_vma_lock_write() doesn't
                                 * help here, as we don't guarantee that all
                                 * growable vmas in a mm share the same root
                                 * anon vma.  So, we reuse mm->page_table_lock
                                 * to guard against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_start = address;
                                vma->vm_pgoff -= grow;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}

/* enforced gap between the expanding stack and other mappings. */
unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;

static int __init cmdline_parse_stack_guard_gap(char *p)
{
        unsigned long val;
        char *endptr;

        val = simple_strtoul(p, &endptr, 10);
        if (!*endptr)
                stack_guard_gap = val << PAGE_SHIFT;

        return 1;
}
__setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);

#ifdef CONFIG_STACK_GROWSUP
int expand_stack_locked(struct vm_area_struct *vma, unsigned long address)
{
        return expand_upwards(vma, address);
}

struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        addr &= PAGE_MASK;
        vma = find_vma_prev(mm, addr, &prev);
        if (vma && (vma->vm_start <= addr))
                return vma;
        if (!prev)
                return NULL;
        if (expand_stack_locked(prev, addr))
                return NULL;
        if (prev->vm_flags & VM_LOCKED)
                populate_vma_page_range(prev, addr, prev->vm_end, NULL);
        return prev;
}
#else
int expand_stack_locked(struct vm_area_struct *vma, unsigned long address)
{
        return expand_downwards(vma, address);
}

struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(mm, addr);
        if (!vma)
                return NULL;
        if (vma->vm_start <= addr)
                return vma;
        start = vma->vm_start;
        if (expand_stack_locked(vma, addr))
                return NULL;
        if (vma->vm_flags & VM_LOCKED)
                populate_vma_page_range(vma, addr, start, NULL);
        return vma;
}
#endif

#if defined(CONFIG_STACK_GROWSUP)

#define vma_expand_up(vma,addr) expand_upwards(vma, addr)
#define vma_expand_down(vma, addr) (-EFAULT)

#else

#define vma_expand_up(vma,addr) (-EFAULT)
#define vma_expand_down(vma, addr) expand_downwards(vma, addr)

#endif

/*
 * expand_stack(): legacy interface for page faulting. Don't use unless
 * you have to.
 *
 * This is called with the mm locked for reading, drops the lock, takes
 * the lock for writing, tries to look up a vma again, expands it if
 * necessary, and downgrades the lock to reading again.
 *
 * If no vma is found or it can't be expanded, it returns NULL and has
 * dropped the lock.
 */
struct vm_area_struct *expand_stack(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        mmap_read_unlock(mm);
        if (mmap_write_lock_killable(mm))
                return NULL;

        vma = find_vma_prev(mm, addr, &prev);
        if (vma && vma->vm_start <= addr)
                goto success;

        if (prev && !vma_expand_up(prev, addr)) {
                vma = prev;
                goto success;
        }

        if (vma && !vma_expand_down(vma, addr))
                goto success;

        mmap_write_unlock(mm);
        return NULL;

success:
        mmap_write_downgrade(mm);
        return vma;
}

/*
 * Ok - we have the memory areas we should free on a maple tree so release them,
 * and do the vma updates.
 *
 * Called with the mm semaphore held.
 */
static inline void remove_mt(struct mm_struct *mm, struct ma_state *mas)
{
        unsigned long nr_accounted = 0;
        struct vm_area_struct *vma;

        /* Update high watermark before we lower total_vm */
        update_hiwater_vm(mm);
        mas_for_each(mas, vma, ULONG_MAX) {
                long nrpages = vma_pages(vma);

                if (vma->vm_flags & VM_ACCOUNT)
                        nr_accounted += nrpages;
                vm_stat_account(mm, vma->vm_flags, -nrpages);
                remove_vma(vma, false);
        }
        vm_unacct_memory(nr_accounted);
}

/*
 * Get rid of page table information in the indicated region.
 *
 * Called with the mm semaphore held.
 */
static void unmap_region(struct mm_struct *mm, struct ma_state *mas,
                struct vm_area_struct *vma, struct vm_area_struct *prev,
                struct vm_area_struct *next, unsigned long start,
                unsigned long end, unsigned long tree_end, bool mm_wr_locked)
{
        struct mmu_gather tlb;
        unsigned long mt_start = mas->index;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        update_hiwater_rss(mm);
        unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked);
        mas_set(mas, mt_start);
        free_pgtables(&tlb, mas, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
                                 next ? next->vm_start : USER_PGTABLES_CEILING,
                                 mm_wr_locked);
        tlb_finish_mmu(&tlb);
}

/*
 * __split_vma() bypasses sysctl_max_map_count checking.  We use this where it
 * has already been checked or doesn't make sense to fail.
 * VMA Iterator will point to the end VMA.
 */
static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
                       unsigned long addr, int new_below)
{
        struct vma_prepare vp;
        struct vm_area_struct *new;
        int err;

        WARN_ON(vma->vm_start >= addr);
        WARN_ON(vma->vm_end <= addr);

        if (vma->vm_ops && vma->vm_ops->may_split) {
                err = vma->vm_ops->may_split(vma, addr);
                if (err)
                        return err;
        }

        new = vm_area_dup(vma);
        if (!new)
                return -ENOMEM;

        if (new_below) {
                new->vm_end = addr;
        } else {
                new->vm_start = addr;
                new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
        }

        err = -ENOMEM;
        vma_iter_config(vmi, new->vm_start, new->vm_end);
        if (vma_iter_prealloc(vmi, new))
                goto out_free_vma;

        err = vma_dup_policy(vma, new);
        if (err)
                goto out_free_vmi;

        err = anon_vma_clone(new, vma);
        if (err)
                goto out_free_mpol;

        if (new->vm_file)
                get_file(new->vm_file);

        if (new->vm_ops && new->vm_ops->open)
                new->vm_ops->open(new);

        vma_start_write(vma);
        vma_start_write(new);

        init_vma_prep(&vp, vma);
        vp.insert = new;
        vma_prepare(&vp);
        vma_adjust_trans_huge(vma, vma->vm_start, addr, 0);

        if (new_below) {
                vma->vm_start = addr;
                vma->vm_pgoff += (addr - new->vm_start) >> PAGE_SHIFT;
        } else {
                vma->vm_end = addr;
        }

        /* vma_complete stores the new vma */
        vma_complete(&vp, vmi, vma->vm_mm);

        /* Success. */
        if (new_below)
                vma_next(vmi);
        return 0;

out_free_mpol:
        mpol_put(vma_policy(new));
out_free_vmi:
        vma_iter_free(vmi);
out_free_vma:
        vm_area_free(new);
        return err;
}

/*
 * Split a vma into two pieces at address 'addr', a new vma is allocated
 * either for the first part or the tail.
 */
static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
                     unsigned long addr, int new_below)
{
        if (vma->vm_mm->map_count >= sysctl_max_map_count)
                return -ENOMEM;

        return __split_vma(vmi, vma, addr, new_below);
}

/*
 * We are about to modify one or multiple of a VMA's flags, policy, userfaultfd
 * context and anonymous VMA name within the range [start, end).
 *
 * As a result, we might be able to merge the newly modified VMA range with an
 * adjacent VMA with identical properties.
 *
 * If no merge is possible and the range does not span the entirety of the VMA,
 * we then need to split the VMA to accommodate the change.
 *
 * The function returns either the merged VMA, the original VMA if a split was
 * required instead, or an error if the split failed.
 */
struct vm_area_struct *vma_modify(struct vma_iterator *vmi,
                                  struct vm_area_struct *prev,
                                  struct vm_area_struct *vma,
                                  unsigned long start, unsigned long end,
                                  unsigned long vm_flags,
                                  struct mempolicy *policy,
                                  struct vm_userfaultfd_ctx uffd_ctx,
                                  struct anon_vma_name *anon_name)
{
        pgoff_t pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
        struct vm_area_struct *merged;

        merged = vma_merge(vmi, prev, vma, start, end, vm_flags,
                           pgoff, policy, uffd_ctx, anon_name);
        if (merged)
                return merged;

        if (vma->vm_start < start) {
                int err = split_vma(vmi, vma, start, 1);

                if (err)
                        return ERR_PTR(err);
        }

        if (vma->vm_end > end) {
                int err = split_vma(vmi, vma, end, 0);

                if (err)
                        return ERR_PTR(err);
        }

        return vma;
}

/*
 * Attempt to merge a newly mapped VMA with those adjacent to it. The caller
 * must ensure that [start, end) does not overlap any existing VMA.
 */
static struct vm_area_struct
*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
                   struct vm_area_struct *vma, unsigned long start,
                   unsigned long end, pgoff_t pgoff)
{
        return vma_merge(vmi, prev, vma, start, end, vma->vm_flags, pgoff,
                         vma_policy(vma), vma->vm_userfaultfd_ctx, anon_vma_name(vma));
}

/*
 * Expand vma by delta bytes, potentially merging with an immediately adjacent
 * VMA with identical properties.
 */
struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
                                        struct vm_area_struct *vma,
                                        unsigned long delta)
{
        pgoff_t pgoff = vma->vm_pgoff + vma_pages(vma);

        /* vma is specified as prev, so case 1 or 2 will apply. */
        return vma_merge(vmi, vma, vma, vma->vm_end, vma->vm_end + delta,
                         vma->vm_flags, pgoff, vma_policy(vma),
                         vma->vm_userfaultfd_ctx, anon_vma_name(vma));
}

/*
 * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
 * @vmi: The vma iterator
 * @vma: The starting vm_area_struct
 * @mm: The mm_struct
 * @start: The aligned start address to munmap.
 * @end: The aligned end address to munmap.
 * @uf: The userfaultfd list_head
 * @unlock: Set to true to drop the mmap_lock.  unlocking only happens on
 * success.
 *
 * Return: 0 on success and drops the lock if so directed, error and leaves the
 * lock held otherwise.
 */
static int
do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
                    struct mm_struct *mm, unsigned long start,
                    unsigned long end, struct list_head *uf, bool unlock)
{
        struct vm_area_struct *prev, *next = NULL;
        struct maple_tree mt_detach;
        int count = 0;
        int error = -ENOMEM;
        unsigned long locked_vm = 0;
        MA_STATE(mas_detach, &mt_detach, 0, 0);
        mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
        mt_on_stack(mt_detach);

        /*
         * If we need to split any vma, do it now to save pain later.
         *
         * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
         * unmapped vm_area_struct will remain in use: so lower split_vma
         * places tmp vma above, and higher split_vma places tmp vma below.
         */

        /* Does it split the first one? */
        if (start > vma->vm_start) {

                /*
                 * Make sure that map_count on return from munmap() will
                 * not exceed its limit; but let map_count go just above
                 * its limit temporarily, to help free resources as expected.
                 */
                if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
                        goto map_count_exceeded;

                error = __split_vma(vmi, vma, start, 1);
                if (error)
                        goto start_split_failed;
        }

        /*
         * Detach a range of VMAs from the mm. Using next as a temp variable as
         * it is always overwritten.
         */
        next = vma;
        do {
                /* Does it split the end? */
                if (next->vm_end > end) {
                        error = __split_vma(vmi, next, end, 0);
                        if (error)
                                goto end_split_failed;
                }
                vma_start_write(next);
                mas_set(&mas_detach, count);
                error = mas_store_gfp(&mas_detach, next, GFP_KERNEL);
                if (error)
                        goto munmap_gather_failed;
                vma_mark_detached(next, true);
                if (next->vm_flags & VM_LOCKED)
                        locked_vm += vma_pages(next);

                count++;
                if (unlikely(uf)) {
                        /*
                         * If userfaultfd_unmap_prep returns an error the vmas
                         * will remain split, but userland will get a
                         * highly unexpected error anyway. This is no
                         * different than the case where the first of the two
                         * __split_vma fails, but we don't undo the first
                         * split, despite we could. This is unlikely enough
                         * failure that it's not worth optimizing it for.
                         */
                        error = userfaultfd_unmap_prep(next, start, end, uf);

                        if (error)
                                goto userfaultfd_error;
                }
#ifdef CONFIG_DEBUG_VM_MAPLE_TREE
                BUG_ON(next->vm_start < start);
                BUG_ON(next->vm_start > end);
#endif
        } for_each_vma_range(*vmi, next, end);

#if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
        /* Make sure no VMAs are about to be lost. */
        {
                MA_STATE(test, &mt_detach, 0, 0);
                struct vm_area_struct *vma_mas, *vma_test;
                int test_count = 0;

                vma_iter_set(vmi, start);
                rcu_read_lock();
                vma_test = mas_find(&test, count - 1);
                for_each_vma_range(*vmi, vma_mas, end) {
                        BUG_ON(vma_mas != vma_test);
                        test_count++;
                        vma_test = mas_next(&test, count - 1);
                }
                rcu_read_unlock();
                BUG_ON(count != test_count);
        }
#endif

        while (vma_iter_addr(vmi) > start)
                vma_iter_prev_range(vmi);

        error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
        if (error)
                goto clear_tree_failed;

        /* Point of no return */
        mm->locked_vm -= locked_vm;
        mm->map_count -= count;
        if (unlock)
                mmap_write_downgrade(mm);

        prev = vma_iter_prev_range(vmi);
        next = vma_next(vmi);
        if (next)
                vma_iter_prev_range(vmi);

        /*
         * We can free page tables without write-locking mmap_lock because VMAs
         * were isolated before we downgraded mmap_lock.
         */
        mas_set(&mas_detach, 1);
        unmap_region(mm, &mas_detach, vma, prev, next, start, end, count,
                     !unlock);
        /* Statistics and freeing VMAs */
        mas_set(&mas_detach, 0);
        remove_mt(mm, &mas_detach);
        validate_mm(mm);
        if (unlock)
                mmap_read_unlock(mm);

        __mt_destroy(&mt_detach);
        return 0;

clear_tree_failed:
userfaultfd_error:
munmap_gather_failed:
end_split_failed:
        mas_set(&mas_detach, 0);
        mas_for_each(&mas_detach, next, end)
                vma_mark_detached(next, false);

        __mt_destroy(&mt_detach);
start_split_failed:
map_count_exceeded:
        validate_mm(mm);
        return error;
}

/*
 * do_vmi_munmap() - munmap a given range.
 * @vmi: The vma iterator
 * @mm: The mm_struct
 * @start: The start address to munmap
 * @len: The length of the range to munmap
 * @uf: The userfaultfd list_head
 * @unlock: set to true if the user wants to drop the mmap_lock on success
 *
 * This function takes a @mas that is either pointing to the previous VMA or set
 * to MA_START and sets it up to remove the mapping(s).  The @len will be
 * aligned and any arch_unmap work will be preformed.
 *
 * Return: 0 on success and drops the lock if so directed, error and leaves the
 * lock held otherwise.
 */
int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
                  unsigned long start, size_t len, struct list_head *uf,
                  bool unlock)
{
        unsigned long end;
        struct vm_area_struct *vma;

        if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
                return -EINVAL;

        end = start + PAGE_ALIGN(len);
        if (end == start)
                return -EINVAL;

         /* arch_unmap() might do unmaps itself.  */
        arch_unmap(mm, start, end);

        /* Find the first overlapping VMA */
        vma = vma_find(vmi, end);
        if (!vma) {
                if (unlock)
                        mmap_write_unlock(mm);
                return 0;
        }

        return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
}

/* do_munmap() - Wrapper function for non-maple tree aware do_munmap() calls.
 * @mm: The mm_struct
 * @start: The start address to munmap
 * @len: The length to be munmapped.
 * @uf: The userfaultfd list_head
 *
 * Return: 0 on success, error otherwise.
 */
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
              struct list_head *uf)
{
        VMA_ITERATOR(vmi, mm, start);

        return do_vmi_munmap(&vmi, mm, start, len, uf, false);
}

unsigned long mmap_region(struct file *file, unsigned long addr,
                unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
                struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = NULL;
        struct vm_area_struct *next, *prev, *merge;
        pgoff_t pglen = len >> PAGE_SHIFT;
        unsigned long charged = 0;
        unsigned long end = addr + len;
        unsigned long merge_start = addr, merge_end = end;
        bool writable_file_mapping = false;
        pgoff_t vm_pgoff;
        int error;
        VMA_ITERATOR(vmi, mm, addr);

        /* Check against address space limit. */
        if (!may_expand_vm(mm, vm_flags, len >> PAGE_SHIFT)) {
                unsigned long nr_pages;

                /*
                 * MAP_FIXED may remove pages of mappings that intersects with
                 * requested mapping. Account for the pages it would unmap.
                 */
                nr_pages = count_vma_pages_range(mm, addr, end);

                if (!may_expand_vm(mm, vm_flags,
                                        (len >> PAGE_SHIFT) - nr_pages))
                        return -ENOMEM;
        }

        /* Unmap any existing mapping in the area */
        if (do_vmi_munmap(&vmi, mm, addr, len, uf, false))
                return -ENOMEM;

        /*
         * Private writable mapping: check memory availability
         */
        if (accountable_mapping(file, vm_flags)) {
                charged = len >> PAGE_SHIFT;
                if (security_vm_enough_memory_mm(mm, charged))
                        return -ENOMEM;
                vm_flags |= VM_ACCOUNT;
        }

        next = vma_next(&vmi);
        prev = vma_prev(&vmi);
        if (vm_flags & VM_SPECIAL) {
                if (prev)
                        vma_iter_next_range(&vmi);
                goto cannot_expand;
        }

        /* Attempt to expand an old mapping */
        /* Check next */
        if (next && next->vm_start == end && !vma_policy(next) &&
            can_vma_merge_before(next, vm_flags, NULL, file, pgoff+pglen,
                                 NULL_VM_UFFD_CTX, NULL)) {
                merge_end = next->vm_end;
                vma = next;
                vm_pgoff = next->vm_pgoff - pglen;
        }

        /* Check prev */
        if (prev && prev->vm_end == addr && !vma_policy(prev) &&
            (vma ? can_vma_merge_after(prev, vm_flags, vma->anon_vma, file,
                                       pgoff, vma->vm_userfaultfd_ctx, NULL) :
                   can_vma_merge_after(prev, vm_flags, NULL, file, pgoff,
                                       NULL_VM_UFFD_CTX, NULL))) {
                merge_start = prev->vm_start;
                vma = prev;
                vm_pgoff = prev->vm_pgoff;
        } else if (prev) {
                vma_iter_next_range(&vmi);
        }

        /* Actually expand, if possible */
        if (vma &&
            !vma_expand(&vmi, vma, merge_start, merge_end, vm_pgoff, next)) {
                khugepaged_enter_vma(vma, vm_flags);
                goto expanded;
        }

        if (vma == prev)
                vma_iter_set(&vmi, addr);
cannot_expand:

        /*
         * Determine the object being mapped and call the appropriate
         * specific mapper. the address has already been validated, but
         * not unmapped, but the maps are removed from the list.
         */
        vma = vm_area_alloc(mm);
        if (!vma) {
                error = -ENOMEM;
                goto unacct_error;
        }

        vma_iter_config(&vmi, addr, end);
        vma_set_range(vma, addr, end, pgoff);
        vm_flags_init(vma, vm_flags);
        vma->vm_page_prot = vm_get_page_prot(vm_flags);

        if (file) {
                vma->vm_file = get_file(file);
                error = call_mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;

                if (vma_is_shared_maywrite(vma)) {
                        error = mapping_map_writable(file->f_mapping);
                        if (error)
                                goto close_and_free_vma;

                        writable_file_mapping = true;
                }

                /*
                 * Expansion is handled above, merging is handled below.
                 * Drivers should not alter the address of the VMA.
                 */
                error = -EINVAL;
                if (WARN_ON((addr != vma->vm_start)))
                        goto close_and_free_vma;

                vma_iter_config(&vmi, addr, end);
                /*
                 * If vm_flags changed after call_mmap(), we should try merge
                 * vma again as we may succeed this time.
                 */
                if (unlikely(vm_flags != vma->vm_flags && prev)) {
                        merge = vma_merge_new_vma(&vmi, prev, vma,
                                                  vma->vm_start, vma->vm_end,
                                                  vma->vm_pgoff);
                        if (merge) {
                                /*
                                 * ->mmap() can change vma->vm_file and fput
                                 * the original file. So fput the vma->vm_file
                                 * here or we would add an extra fput for file
                                 * and cause general protection fault
                                 * ultimately.
                                 */
                                fput(vma->vm_file);
                                vm_area_free(vma);
                                vma = merge;
                                /* Update vm_flags to pick up the change. */
                                vm_flags = vma->vm_flags;
                                goto unmap_writable;
                        }
                }

                vm_flags = vma->vm_flags;
        } else if (vm_flags & VM_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
                        goto free_vma;
        } else {
                vma_set_anonymous(vma);
        }

        if (map_deny_write_exec(vma, vma->vm_flags)) {
                error = -EACCES;
                goto close_and_free_vma;
        }

        /* Allow architectures to sanity-check the vm_flags */
        error = -EINVAL;
        if (!arch_validate_flags(vma->vm_flags))
                goto close_and_free_vma;

        error = -ENOMEM;
        if (vma_iter_prealloc(&vmi, vma))
                goto close_and_free_vma;

        /* Lock the VMA since it is modified after insertion into VMA tree */
        vma_start_write(vma);
        vma_iter_store(&vmi, vma);
        mm->map_count++;
        vma_link_file(vma);

        /*
         * vma_merge() calls khugepaged_enter_vma() either, the below
         * call covers the non-merge case.
         */
        khugepaged_enter_vma(vma, vma->vm_flags);

        /* Once vma denies write, undo our temporary denial count */
unmap_writable:
        if (writable_file_mapping)
                mapping_unmap_writable(file->f_mapping);
        file = vma->vm_file;
        ksm_add_vma(vma);
expanded:
        perf_event_mmap(vma);

        vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
        if (vm_flags & VM_LOCKED) {
                if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
                                        is_vm_hugetlb_page(vma) ||
                                        vma == get_gate_vma(current->mm))
                        vm_flags_clear(vma, VM_LOCKED_MASK);
                else
                        mm->locked_vm += (len >> PAGE_SHIFT);
        }

        if (file)
                uprobe_mmap(vma);

        /*
         * New (or expanded) vma always get soft dirty status.
         * Otherwise user-space soft-dirty page tracker won't
         * be able to distinguish situation when vma area unmapped,
         * then new mapped in-place (which must be aimed as
         * a completely new data area).
         */
        vm_flags_set(vma, VM_SOFTDIRTY);

        vma_set_page_prot(vma);

        validate_mm(mm);
        return addr;

close_and_free_vma:
        if (file && vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);

        if (file || vma->vm_file) {
unmap_and_free_vma:
                fput(vma->vm_file);
                vma->vm_file = NULL;

                vma_iter_set(&vmi, vma->vm_end);
                /* Undo any partial mapping done by a device driver. */
                unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start,
                             vma->vm_end, vma->vm_end, true);
        }
        if (writable_file_mapping)
                mapping_unmap_writable(file->f_mapping);
free_vma:
        vm_area_free(vma);
unacct_error:
        if (charged)
                vm_unacct_memory(charged);
        validate_mm(mm);
        return error;
}

static int __vm_munmap(unsigned long start, size_t len, bool unlock)
{
        int ret;
        struct mm_struct *mm = current->mm;
        LIST_HEAD(uf);
        VMA_ITERATOR(vmi, mm, start);

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = do_vmi_munmap(&vmi, mm, start, len, &uf, unlock);
        if (ret || !unlock)
                mmap_write_unlock(mm);

        userfaultfd_unmap_complete(mm, &uf);
        return ret;
}

int vm_munmap(unsigned long start, size_t len)
{
        return __vm_munmap(start, len, false);
}
EXPORT_SYMBOL(vm_munmap);

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
        addr = untagged_addr(addr);
        return __vm_munmap(addr, len, true);
}


/*
 * Emulation of deprecated remap_file_pages() syscall.
 */
SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
{

        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long populate = 0;
        unsigned long ret = -EINVAL;
        struct file *file;

        pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. See Documentation/mm/remap_file_pages.rst.\n",
                     current->comm, current->pid);

        if (prot)
                return ret;
        start = start & PAGE_MASK;
        size = size & PAGE_MASK;

        if (start + size <= start)
                return ret;

        /* Does pgoff wrap? */
        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
                return ret;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        vma = vma_lookup(mm, start);

        if (!vma || !(vma->vm_flags & VM_SHARED))
                goto out;

        if (start + size > vma->vm_end) {
                VMA_ITERATOR(vmi, mm, vma->vm_end);
                struct vm_area_struct *next, *prev = vma;

                for_each_vma_range(vmi, next, start + size) {
                        /* hole between vmas ? */
                        if (next->vm_start != prev->vm_end)
                                goto out;

                        if (next->vm_file != vma->vm_file)
                                goto out;

                        if (next->vm_flags != vma->vm_flags)
                                goto out;

                        if (start + size <= next->vm_end)
                                break;

                        prev = next;
                }

                if (!next)
                        goto out;
        }

        prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;
        prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0;
        prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0;

        flags &= MAP_NONBLOCK;
        flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
        if (vma->vm_flags & VM_LOCKED)
                flags |= MAP_LOCKED;

        file = get_file(vma->vm_file);
        ret = do_mmap(vma->vm_file, start, size,
                        prot, flags, 0, pgoff, &populate, NULL);
        fput(file);
out:
        mmap_write_unlock(mm);
        if (populate)
                mm_populate(ret, populate);
        if (!IS_ERR_VALUE(ret))
                ret = 0;
        return ret;
}

/*
 * do_vma_munmap() - Unmap a full or partial vma.
 * @vmi: The vma iterator pointing at the vma
 * @vma: The first vma to be munmapped
 * @start: the start of the address to unmap
 * @end: The end of the address to unmap
 * @uf: The userfaultfd list_head
 * @unlock: Drop the lock on success
 *
 * unmaps a VMA mapping when the vma iterator is already in position.
 * Does not handle alignment.
 *
 * Return: 0 on success drops the lock of so directed, error on failure and will
 * still hold the lock.
 */
int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
                unsigned long start, unsigned long end, struct list_head *uf,
                bool unlock)
{
        struct mm_struct *mm = vma->vm_mm;

        arch_unmap(mm, start, end);
        return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
}

/*
 * do_brk_flags() - Increase the brk vma if the flags match.
 * @vmi: The vma iterator
 * @addr: The start address
 * @len: The length of the increase
 * @vma: The vma,
 * @flags: The VMA Flags
 *
 * Extend the brk VMA from addr to addr + len.  If the VMA is NULL or the flags
 * do not match then create a new anonymous VMA.  Eventually we may be able to
 * do some brk-specific accounting here.
 */
static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
                unsigned long addr, unsigned long len, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vma_prepare vp;

        /*
         * Check against address space limits by the changed size
         * Note: This happens *after* clearing old mappings in some code paths.
         */
        flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
        if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))
                return -ENOMEM;

        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
                return -ENOMEM;

        /*
         * Expand the existing vma if possible; Note that singular lists do not
         * occur after forking, so the expand will only happen on new VMAs.
         */
        if (vma && vma->vm_end == addr && !vma_policy(vma) &&
            can_vma_merge_after(vma, flags, NULL, NULL,
                                addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL)) {
                vma_iter_config(vmi, vma->vm_start, addr + len);
                if (vma_iter_prealloc(vmi, vma))
                        goto unacct_fail;

                vma_start_write(vma);

                init_vma_prep(&vp, vma);
                vma_prepare(&vp);
                vma_adjust_trans_huge(vma, vma->vm_start, addr + len, 0);
                vma->vm_end = addr + len;
                vm_flags_set(vma, VM_SOFTDIRTY);
                vma_iter_store(vmi, vma);

                vma_complete(&vp, vmi, mm);
                khugepaged_enter_vma(vma, flags);
                goto out;
        }

        if (vma)
                vma_iter_next_range(vmi);
        /* create a vma struct for an anonymous mapping */
        vma = vm_area_alloc(mm);
        if (!vma)
                goto unacct_fail;

        vma_set_anonymous(vma);
        vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT);
        vm_flags_init(vma, flags);
        vma->vm_page_prot = vm_get_page_prot(flags);
        vma_start_write(vma);
        if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
                goto mas_store_fail;

        mm->map_count++;
        validate_mm(mm);
        ksm_add_vma(vma);
out:
        perf_event_mmap(vma);
        mm->total_vm += len >> PAGE_SHIFT;
        mm->data_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED)
                mm->locked_vm += (len >> PAGE_SHIFT);
        vm_flags_set(vma, VM_SOFTDIRTY);
        return 0;

mas_store_fail:
        vm_area_free(vma);
unacct_fail:
        vm_unacct_memory(len >> PAGE_SHIFT);
        return -ENOMEM;
}

int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = NULL;
        unsigned long len;
        int ret;
        bool populate;
        LIST_HEAD(uf);
        VMA_ITERATOR(vmi, mm, addr);

        len = PAGE_ALIGN(request);
        if (len < request)
                return -ENOMEM;
        if (!len)
                return 0;

        /* Until we need other flags, refuse anything except VM_EXEC. */
        if ((flags & (~VM_EXEC)) != 0)
                return -EINVAL;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = check_brk_limits(addr, len);
        if (ret)
                goto limits_failed;

        ret = do_vmi_munmap(&vmi, mm, addr, len, &uf, 0);
        if (ret)
                goto munmap_failed;

        vma = vma_prev(&vmi);
        ret = do_brk_flags(&vmi, vma, addr, len, flags);
        populate = ((mm->def_flags & VM_LOCKED) != 0);
        mmap_write_unlock(mm);
        userfaultfd_unmap_complete(mm, &uf);
        if (populate && !ret)
                mm_populate(addr, len);
        return ret;

munmap_failed:
limits_failed:
        mmap_write_unlock(mm);
        return ret;
}
EXPORT_SYMBOL(vm_brk_flags);

/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
        struct mmu_gather tlb;
        struct vm_area_struct *vma;
        unsigned long nr_accounted = 0;
        VMA_ITERATOR(vmi, mm, 0);
        int count = 0;

        /* mm's last user has gone, and its about to be pulled down */
        mmu_notifier_release(mm);

        mmap_read_lock(mm);
        arch_exit_mmap(mm);

        vma = vma_next(&vmi);
        if (!vma || unlikely(xa_is_zero(vma))) {
                /* Can happen if dup_mmap() received an OOM */
                mmap_read_unlock(mm);
                mmap_write_lock(mm);
                goto destroy;
        }

        lru_add_drain();
        flush_cache_mm(mm);
        tlb_gather_mmu_fullmm(&tlb, mm);
        /* update_hiwater_rss(mm) here? but nobody should be looking */
        /* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
        unmap_vmas(&tlb, &vmi.mas, vma, 0, ULONG_MAX, ULONG_MAX, false);
        mmap_read_unlock(mm);

        /*
         * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
         * because the memory has been already freed.
         */
        set_bit(MMF_OOM_SKIP, &mm->flags);
        mmap_write_lock(mm);
        mt_clear_in_rcu(&mm->mm_mt);
        vma_iter_set(&vmi, vma->vm_end);
        free_pgtables(&tlb, &vmi.mas, vma, FIRST_USER_ADDRESS,
                      USER_PGTABLES_CEILING, true);
        tlb_finish_mmu(&tlb);

        /*
         * Walk the list again, actually closing and freeing it, with preemption
         * enabled, without holding any MM locks besides the unreachable
         * mmap_write_lock.
         */
        vma_iter_set(&vmi, vma->vm_end);
        do {
                if (vma->vm_flags & VM_ACCOUNT)
                        nr_accounted += vma_pages(vma);
                remove_vma(vma, true);
                count++;
                cond_resched();
                vma = vma_next(&vmi);
        } while (vma && likely(!xa_is_zero(vma)));

        BUG_ON(count != mm->map_count);

        trace_exit_mmap(mm);
destroy:
        __mt_destroy(&mm->mm_mt);
        mmap_write_unlock(mm);
        vm_unacct_memory(nr_accounted);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap tree.  If vm_file is non-NULL
 * then i_mmap_rwsem is taken here.
 */
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
        unsigned long charged = vma_pages(vma);


        if (find_vma_intersection(mm, vma->vm_start, vma->vm_end))
                return -ENOMEM;

        if ((vma->vm_flags & VM_ACCOUNT) &&
             security_vm_enough_memory_mm(mm, charged))
                return -ENOMEM;

        /*
         * The vm_pgoff of a purely anonymous vma should be irrelevant
         * until its first write fault, when page's anon_vma and index
         * are set.  But now set the vm_pgoff it will almost certainly
         * end up with (unless mremap moves it elsewhere before that
         * first wfault), so /proc/pid/maps tells a consistent story.
         *
         * By setting it to reflect the virtual start address of the
         * vma, merges and splits can happen in a seamless way, just
         * using the existing file pgoff checks and manipulations.
         * Similarly in do_mmap and in do_brk_flags.
         */
        if (vma_is_anonymous(vma)) {
                BUG_ON(vma->anon_vma);
                vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
        }

        if (vma_link(mm, vma)) {
                if (vma->vm_flags & VM_ACCOUNT)
                        vm_unacct_memory(charged);
                return -ENOMEM;
        }

        return 0;
}

/*
 * Copy the vma structure to a new location in the same mm,
 * prior to moving page table entries, to effect an mremap move.
 */
struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
        unsigned long addr, unsigned long len, pgoff_t pgoff,
        bool *need_rmap_locks)
{
        struct vm_area_struct *vma = *vmap;
        unsigned long vma_start = vma->vm_start;
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma, *prev;
        bool faulted_in_anon_vma = true;
        VMA_ITERATOR(vmi, mm, addr);

        /*
         * If anonymous vma has not yet been faulted, update new pgoff
         * to match new location, to increase its chance of merging.
         */
        if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) {
                pgoff = addr >> PAGE_SHIFT;
                faulted_in_anon_vma = false;
        }

        new_vma = find_vma_prev(mm, addr, &prev);
        if (new_vma && new_vma->vm_start < addr + len)
                return NULL;    /* should never get here */

        new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
        if (new_vma) {
                /*
                 * Source vma may have been merged into new_vma
                 */
                if (unlikely(vma_start >= new_vma->vm_start &&
                             vma_start < new_vma->vm_end)) {
                        /*
                         * The only way we can get a vma_merge with
                         * self during an mremap is if the vma hasn't
                         * been faulted in yet and we were allowed to
                         * reset the dst vma->vm_pgoff to the
                         * destination address of the mremap to allow
                         * the merge to happen. mremap must change the
                         * vm_pgoff linearity between src and dst vmas
                         * (in turn preventing a vma_merge) to be
                         * safe. It is only safe to keep the vm_pgoff
                         * linear if there are no pages mapped yet.
                         */
                        VM_BUG_ON_VMA(faulted_in_anon_vma, new_vma);
                        *vmap = vma = new_vma;
                }
                *need_rmap_locks = (new_vma->vm_pgoff <= vma->vm_pgoff);
        } else {
                new_vma = vm_area_dup(vma);
                if (!new_vma)
                        goto out;
                vma_set_range(new_vma, addr, addr + len, pgoff);
                if (vma_dup_policy(vma, new_vma))
                        goto out_free_vma;
                if (anon_vma_clone(new_vma, vma))
                        goto out_free_mempol;
                if (new_vma->vm_file)
                        get_file(new_vma->vm_file);
                if (new_vma->vm_ops && new_vma->vm_ops->open)
                        new_vma->vm_ops->open(new_vma);
                if (vma_link(mm, new_vma))
                        goto out_vma_link;
                *need_rmap_locks = false;
        }
        return new_vma;

out_vma_link:
        if (new_vma->vm_ops && new_vma->vm_ops->close)
                new_vma->vm_ops->close(new_vma);

        if (new_vma->vm_file)
                fput(new_vma->vm_file);

        unlink_anon_vmas(new_vma);
out_free_mempol:
        mpol_put(vma_policy(new_vma));
out_free_vma:
        vm_area_free(new_vma);
out:
        return NULL;
}

/*
 * Return true if the calling process may expand its vm space by the passed
 * number of pages
 */
bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
{
        if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
                return false;

        if (is_data_mapping(flags) &&
            mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT) {
                /* Workaround for Valgrind */
                if (rlimit(RLIMIT_DATA) == 0 &&
                    mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
                        return true;

                pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits%s.\n",
                             current->comm, current->pid,
                             (mm->data_vm + npages) << PAGE_SHIFT,
                             rlimit(RLIMIT_DATA),
                             ignore_rlimit_data ? "" : " or use boot option ignore_rlimit_data");

                if (!ignore_rlimit_data)
                        return false;
        }

        return true;
}

void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
{
        WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm)+npages);

        if (is_exec_mapping(flags))
                mm->exec_vm += npages;
        else if (is_stack_mapping(flags))
                mm->stack_vm += npages;
        else if (is_data_mapping(flags))
                mm->data_vm += npages;
}

static vm_fault_t special_mapping_fault(struct vm_fault *vmf);

/*
 * Having a close hook prevents vma merging regardless of flags.
 */
static void special_mapping_close(struct vm_area_struct *vma)
{
}

static const char *special_mapping_name(struct vm_area_struct *vma)
{
        return ((struct vm_special_mapping *)vma->vm_private_data)->name;
}

static int special_mapping_mremap(struct vm_area_struct *new_vma)
{
        struct vm_special_mapping *sm = new_vma->vm_private_data;

        if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
                return -EFAULT;

        if (sm->mremap)
                return sm->mremap(sm, new_vma);

        return 0;
}

static int special_mapping_split(struct vm_area_struct *vma, unsigned long addr)
{
        /*
         * Forbid splitting special mappings - kernel has expectations over
         * the number of pages in mapping. Together with VM_DONTEXPAND
         * the size of vma should stay the same over the special mapping's
         * lifetime.
         */
        return -EINVAL;
}

static const struct vm_operations_struct special_mapping_vmops = {
        .close = special_mapping_close,
        .fault = special_mapping_fault,
        .mremap = special_mapping_mremap,
        .name = special_mapping_name,
        /* vDSO code relies that VVAR can't be accessed remotely */
        .access = NULL,
        .may_split = special_mapping_split,
};

static const struct vm_operations_struct legacy_special_mapping_vmops = {
        .close = special_mapping_close,
        .fault = special_mapping_fault,
};

static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        pgoff_t pgoff;
        struct page **pages;

        if (vma->vm_ops == &legacy_special_mapping_vmops) {
                pages = vma->vm_private_data;
        } else {
                struct vm_special_mapping *sm = vma->vm_private_data;

                if (sm->fault)
                        return sm->fault(sm, vmf->vma, vmf);

                pages = sm->pages;
        }

        for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
                pgoff--;

        if (*pages) {
                struct page *page = *pages;
                get_page(page);
                vmf->page = page;
                return 0;
        }

        return VM_FAULT_SIGBUS;
}

static struct vm_area_struct *__install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, void *priv,
        const struct vm_operations_struct *ops)
{
        int ret;
        struct vm_area_struct *vma;

        vma = vm_area_alloc(mm);
        if (unlikely(vma == NULL))
                return ERR_PTR(-ENOMEM);

        vma_set_range(vma, addr, addr + len, 0);
        vm_flags_init(vma, (vm_flags | mm->def_flags |
                      VM_DONTEXPAND | VM_SOFTDIRTY) & ~VM_LOCKED_MASK);
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

        vma->vm_ops = ops;
        vma->vm_private_data = priv;

        ret = insert_vm_struct(mm, vma);
        if (ret)
                goto out;

        vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);

        perf_event_mmap(vma);

        return vma;

out:
        vm_area_free(vma);
        return ERR_PTR(ret);
}

bool vma_is_special_mapping(const struct vm_area_struct *vma,
        const struct vm_special_mapping *sm)
{
        return vma->vm_private_data == sm &&
                (vma->vm_ops == &special_mapping_vmops ||
                 vma->vm_ops == &legacy_special_mapping_vmops);
}

/*
 * Called with mm->mmap_lock held for writing.
 * Insert a new vma covering the given region, with the given flags.
 * Its pages are supplied by the given array of struct page *.
 * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
 * The region past the last page supplied will always produce SIGBUS.
 * The array pointer and the pages it points to are assumed to stay alive
 * for as long as this mapping might exist.
 */
struct vm_area_struct *_install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, const struct vm_special_mapping *spec)
{
        return __install_special_mapping(mm, addr, len, vm_flags, (void *)spec,
                                        &special_mapping_vmops);
}

int install_special_mapping(struct mm_struct *mm,
                            unsigned long addr, unsigned long len,
                            unsigned long vm_flags, struct page **pages)
{
        struct vm_area_struct *vma = __install_special_mapping(
                mm, addr, len, vm_flags, (void *)pages,
                &legacy_special_mapping_vmops);

        return PTR_ERR_OR_ZERO(vma);
}

static DEFINE_MUTEX(mm_all_locks_mutex);

static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
{
        if (!test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
                /*
                 * The LSB of head.next can't change from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock);
                /*
                 * We can safely modify head.next after taking the
                 * anon_vma->root->rwsem. If some other vma in this mm shares
                 * the same anon_vma we won't take it again.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us thanks to the
                 * anon_vma->root->rwsem.
                 */
                if (__test_and_set_bit(0, (unsigned long *)
                                       &anon_vma->root->rb_root.rb_root.rb_node))
                        BUG();
        }
}

static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
{
        if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change from under us because
                 * we hold the mm_all_locks_mutex.
                 *
                 * Operations on ->flags have to be atomic because
                 * even if AS_MM_ALL_LOCKS is stable thanks to the
                 * mm_all_locks_mutex, there may be other cpus
                 * changing other bitflags in parallel to us.
                 */
                if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
                        BUG();
                down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock);
        }
}

/*
 * This operation locks against the VM for all pte/vma/mm related
 * operations that could ever happen on a certain mm. This includes
 * vmtruncate, try_to_unmap, and all page faults.
 *
 * The caller must take the mmap_lock in write mode before calling
 * mm_take_all_locks(). The caller isn't allowed to release the
 * mmap_lock until mm_drop_all_locks() returns.
 *
 * mmap_lock in write mode is required in order to block all operations
 * that could modify pagetables and free pages without need of
 * altering the vma layout. It's also needed in write mode to avoid new
 * anon_vmas to be associated with existing vmas.
 *
 * A single task can't take more than one mm_take_all_locks() in a row
 * or it would deadlock.
 *
 * The LSB in anon_vma->rb_root.rb_node and the AS_MM_ALL_LOCKS bitflag in
 * mapping->flags avoid to take the same lock twice, if more than one
 * vma in this mm is backed by the same anon_vma or address_space.
 *
 * We take locks in following order, accordingly to comment at beginning
 * of mm/rmap.c:
 *   - all hugetlbfs_i_mmap_rwsem_key locks (aka mapping->i_mmap_rwsem for
 *     hugetlb mapping);
 *   - all vmas marked locked
 *   - all i_mmap_rwsem locks;
 *   - all anon_vma->rwseml
 *
 * We can take all locks within these types randomly because the VM code
 * doesn't nest them and we protected from parallel mm_take_all_locks() by
 * mm_all_locks_mutex.
 *
 * mm_take_all_locks() and mm_drop_all_locks are expensive operations
 * that may have to take thousand of locks.
 *
 * mm_take_all_locks() can fail if it's interrupted by signals.
 */
int mm_take_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        struct anon_vma_chain *avc;
        VMA_ITERATOR(vmi, mm, 0);

        mmap_assert_write_locked(mm);

        mutex_lock(&mm_all_locks_mutex);

        /*
         * vma_start_write() does not have a complement in mm_drop_all_locks()
         * because vma_start_write() is always asymmetrical; it marks a VMA as
         * being written to until mmap_write_unlock() or mmap_write_downgrade()
         * is reached.
         */
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                vma_start_write(vma);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->vm_file && vma->vm_file->f_mapping &&
                                !is_vm_hugetlb_page(vma))
                        vm_lock_mapping(mm, vma->vm_file->f_mapping);
        }

        vma_iter_init(&vmi, mm, 0);
        for_each_vma(vmi, vma) {
                if (signal_pending(current))
                        goto out_unlock;
                if (vma->anon_vma)
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                vm_lock_anon_vma(mm, avc->anon_vma);
        }

        return 0;

out_unlock:
        mm_drop_all_locks(mm);
        return -EINTR;
}

static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
{
        if (test_bit(0, (unsigned long *) &anon_vma->root->rb_root.rb_root.rb_node)) {
                /*
                 * The LSB of head.next can't change to 0 from under
                 * us because we hold the mm_all_locks_mutex.
                 *
                 * We must however clear the bitflag before unlocking
                 * the vma so the users using the anon_vma->rb_root will
                 * never see our bitflag.
                 *
                 * No need of atomic instructions here, head.next
                 * can't change from under us until we release the
                 * anon_vma->root->rwsem.
                 */
                if (!__test_and_clear_bit(0, (unsigned long *)
                                          &anon_vma->root->rb_root.rb_root.rb_node))
                        BUG();
                anon_vma_unlock_write(anon_vma);
        }
}

static void vm_unlock_mapping(struct address_space *mapping)
{
        if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
                /*
                 * AS_MM_ALL_LOCKS can't change to 0 from under us
                 * because we hold the mm_all_locks_mutex.
                 */
                i_mmap_unlock_write(mapping);
                if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
                                        &mapping->flags))
                        BUG();
        }
}

/*
 * The mmap_lock cannot be released by the caller until
 * mm_drop_all_locks() returns.
 */
void mm_drop_all_locks(struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        struct anon_vma_chain *avc;
        VMA_ITERATOR(vmi, mm, 0);

        mmap_assert_write_locked(mm);
        BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));

        for_each_vma(vmi, vma) {
                if (vma->anon_vma)
                        list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                                vm_unlock_anon_vma(avc->anon_vma);
                if (vma->vm_file && vma->vm_file->f_mapping)
                        vm_unlock_mapping(vma->vm_file->f_mapping);
        }

        mutex_unlock(&mm_all_locks_mutex);
}

/*
 * initialise the percpu counter for VM
 */
void __init mmap_init(void)
{
        int ret;

        ret = percpu_counter_init(&vm_committed_as, 0, GFP_KERNEL);
        VM_BUG_ON(ret);
}

/*
 * Initialise sysctl_user_reserve_kbytes.
 *
 * This is intended to prevent a user from starting a single memory hogging
 * process, such that they cannot recover (kill the hog) in OVERCOMMIT_NEVER
 * mode.
 *
 * The default value is min(3% of free memory, 128MB)
 * 128MB is enough to recover with sshd/login, bash, and top/kill.
 */
static int init_user_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

        sysctl_user_reserve_kbytes = min(free_kbytes / 32, SZ_128K);
        return 0;
}
subsys_initcall(init_user_reserve);

/*
 * Initialise sysctl_admin_reserve_kbytes.
 *
 * The purpose of sysctl_admin_reserve_kbytes is to allow the sys admin
 * to log in and kill a memory hogging process.
 *
 * Systems with more than 256MB will reserve 8MB, enough to recover
 * with sshd, bash, and top in OVERCOMMIT_GUESS. Smaller systems will
 * only reserve 3% of free pages by default.
 */
static int init_admin_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

        sysctl_admin_reserve_kbytes = min(free_kbytes / 32, SZ_8K);
        return 0;
}
subsys_initcall(init_admin_reserve);

/*
 * Reinititalise user and admin reserves if memory is added or removed.
 *
 * The default user reserve max is 128MB, and the default max for the
 * admin reserve is 8MB. These are usually, but not always, enough to
 * enable recovery from a memory hogging process using login/sshd, a shell,
 * and tools like top. It may make sense to increase or even disable the
 * reserve depending on the existence of swap or variations in the recovery
 * tools. So, the admin may have changed them.
 *
 * If memory is added and the reserves have been eliminated or increased above
 * the default max, then we'll trust the admin.
 *
 * If memory is removed and there isn't enough free memory, then we
 * need to reset the reserves.
 *
 * Otherwise keep the reserve set by the admin.
 */
static int reserve_mem_notifier(struct notifier_block *nb,
                             unsigned long action, void *data)
{
        unsigned long tmp, free_kbytes;

        switch (action) {
        case MEM_ONLINE:
                /* Default max is 128MB. Leave alone if modified by operator. */
                tmp = sysctl_user_reserve_kbytes;
                if (tmp > 0 && tmp < SZ_128K)
                        init_user_reserve();

                /* Default max is 8MB.  Leave alone if modified by operator. */
                tmp = sysctl_admin_reserve_kbytes;
                if (tmp > 0 && tmp < SZ_8K)
                        init_admin_reserve();

                break;
        case MEM_OFFLINE:
                free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

                if (sysctl_user_reserve_kbytes > free_kbytes) {
                        init_user_reserve();
                        pr_info("vm.user_reserve_kbytes reset to %lu\n",
                                sysctl_user_reserve_kbytes);
                }

                if (sysctl_admin_reserve_kbytes > free_kbytes) {
                        init_admin_reserve();
                        pr_info("vm.admin_reserve_kbytes reset to %lu\n",
                                sysctl_admin_reserve_kbytes);
                }
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static int __meminit init_reserve_notifier(void)
{
        if (hotplug_memory_notifier(reserve_mem_notifier, DEFAULT_CALLBACK_PRI))
                pr_err("Failed registering memory add/remove notifier for admin reserve\n");

        return 0;
}
subsys_initcall(init_reserve_notifier);