mm/hugetlb: introduce hugetlb_walk()

huge_pte_offset() is the main walker function for hugetlb pgtables.  The
name is not really representing what it does, though.

Instead of renaming it, introduce a wrapper function called hugetlb_walk()
which will use huge_pte_offset() inside.  Assert on the locks when walking
the pgtable.

Note, the vma lock assertion will be a no-op for private mappings.

Document the last special case in the page_vma_mapped_walk() path where we
don't need any more lock to call hugetlb_walk().

Taking vma lock there is not needed because either: (1) potential callers
of hugetlb pvmw holds i_mmap_rwsem already (from one rmap_walk()), or (2)
the caller will not walk a hugetlb vma at all so the hugetlb code path not
reachable (e.g.  in ksm or uprobe paths).

It's slightly implicit for future page_vma_mapped_walk() callers on that
lock requirement.  But anyway, when one day this rule breaks, one will get
a straightforward warning in hugetlb_walk() with lockdep, then there'll be
a way out.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20221216155229.2043750-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index fdb16246f46ecb32fc63758c7fba213b7d4042df..48f1a8ad22431e82660da5e51b8c863dfe118a6f 100644 (file)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -388,9 +388,7 @@ static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
 {
        pte_t *ptep, pte;
 
-       ptep = huge_pte_offset(vma->vm_mm, addr,
-                       huge_page_size(hstate_vma(vma)));
-
+       ptep = hugetlb_walk(vma, addr, huge_page_size(hstate_vma(vma)));
        if (!ptep)
                return false;
 

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 3b1797e0448a5d1b85f7608343a6ba8b0f8c4eae..15a5bf765d432739d22774ed9b45bc5d805b4eb1 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -252,14 +252,12 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
                                         unsigned long flags,
                                         unsigned long reason)
 {
-       struct mm_struct *mm = ctx->mm;
        pte_t *ptep, pte;
        bool ret = true;
 
-       mmap_assert_locked(mm);
-
-       ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
+       mmap_assert_locked(ctx->mm);
 
+       ptep = hugetlb_walk(vma, address, vma_mmu_pagesize(vma));
        if (!ptep)
                goto out;
 

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index d755e2a7c0db0723a1acf9fe01becd6b19061836..b6b10101bea725323cda960ddd06682854eb3629 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_HUGETLB_H
 #define _LINUX_HUGETLB_H
 
+#include <linux/mm.h>
 #include <linux/mm_types.h>
 #include <linux/mmdebug.h>
 #include <linux/fs.h>
@@ -196,6 +197,11 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
  * huge_pte_offset(): Walk the hugetlb pgtable until the last level PTE.
  * Returns the pte_t* if found, or NULL if the address is not mapped.
  *
+ * IMPORTANT: we should normally not directly call this function, instead
+ * this is only a common interface to implement arch-specific
+ * walker. Please use hugetlb_walk() instead, because that will attempt to
+ * verify the locking for you.
+ *
  * Since this function will walk all the pgtable pages (including not only
  * high-level pgtable page, but also PUD entry that can be unshared
  * concurrently for VM_SHARED), the caller of this function should be
@@ -1229,4 +1235,35 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr);
 #define flush_hugetlb_tlb_range(vma, addr, end)        flush_tlb_range(vma, addr, end)
 #endif
 
+static inline bool __vma_shareable_lock(struct vm_area_struct *vma)
+{
+       return (vma->vm_flags & VM_MAYSHARE) && vma->vm_private_data;
+}
+
+/*
+ * Safe version of huge_pte_offset() to check the locks.  See comments
+ * above huge_pte_offset().
+ */
+static inline pte_t *
+hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz)
+{
+#if defined(CONFIG_HUGETLB_PAGE) && \
+       defined(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && defined(CONFIG_LOCKDEP)
+       struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
+
+       /*
+        * If pmd sharing possible, locking needed to safely walk the
+        * hugetlb pgtables.  More information can be found at the comment
+        * above huge_pte_offset() in the same file.
+        *
+        * NOTE: lockdep_is_held() is only defined with CONFIG_LOCKDEP.
+        */
+       if (__vma_shareable_lock(vma))
+               WARN_ON_ONCE(!lockdep_is_held(&vma_lock->rw_sema) &&
+                            !lockdep_is_held(
+                                &vma->vm_file->f_mapping->i_mmap_rwsem));
+#endif
+       return huge_pte_offset(vma->vm_mm, addr, sz);
+}
+
 #endif /* _LINUX_HUGETLB_H */

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index da4c37553c08cc6c690128d15028636baa3fede4..0e5441d6890abcc63bd632c622f08ec75b538b8d 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -260,11 +260,6 @@ static inline struct hugepage_subpool *subpool_vma(struct vm_area_struct *vma)
 /*
  * hugetlb vma_lock helper routines
  */
-static bool __vma_shareable_lock(struct vm_area_struct *vma)
-{
-       return vma->vm_flags & VM_MAYSHARE && vma->vm_private_data;
-}
-
 void hugetlb_vma_lock_read(struct vm_area_struct *vma)
 {
        if (__vma_shareable_lock(vma)) {
@@ -4980,7 +4975,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
        } else {
                /*
                 * For shared mappings the vma lock must be held before
-                * calling huge_pte_offset in the src vma. Otherwise, the
+                * calling hugetlb_walk() in the src vma. Otherwise, the
                 * returned ptep could go away if part of a shared pmd and
                 * another thread calls huge_pmd_unshare.
                 */
@@ -4990,7 +4985,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
        last_addr_mask = hugetlb_mask_last_page(h);
        for (addr = src_vma->vm_start; addr < src_vma->vm_end; addr += sz) {
                spinlock_t *src_ptl, *dst_ptl;
-               src_pte = huge_pte_offset(src, addr, sz);
+               src_pte = hugetlb_walk(src_vma, addr, sz);
                if (!src_pte) {
                        addr |= last_addr_mask;
                        continue;
@@ -5197,7 +5192,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma,
        hugetlb_vma_lock_write(vma);
        i_mmap_lock_write(mapping);
        for (; old_addr < old_end; old_addr += sz, new_addr += sz) {
-               src_pte = huge_pte_offset(mm, old_addr, sz);
+               src_pte = hugetlb_walk(vma, old_addr, sz);
                if (!src_pte) {
                        old_addr |= last_addr_mask;
                        new_addr |= last_addr_mask;
@@ -5260,7 +5255,7 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
        last_addr_mask = hugetlb_mask_last_page(h);
        address = start;
        for (; address < end; address += sz) {
-               ptep = huge_pte_offset(mm, address, sz);
+               ptep = hugetlb_walk(vma, address, sz);
                if (!ptep) {
                        address |= last_addr_mask;
                        continue;
@@ -5573,7 +5568,7 @@ retry_avoidcopy:
                        mutex_lock(&hugetlb_fault_mutex_table[hash]);
                        hugetlb_vma_lock_read(vma);
                        spin_lock(ptl);
-                       ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
+                       ptep = hugetlb_walk(vma, haddr, huge_page_size(h));
                        if (likely(ptep &&
                                   pte_same(huge_ptep_get(ptep), pte)))
                                goto retry_avoidcopy;
@@ -5611,7 +5606,7 @@ retry_avoidcopy:
         * before the page tables are altered
         */
        spin_lock(ptl);
-       ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
+       ptep = hugetlb_walk(vma, haddr, huge_page_size(h));
        if (likely(ptep && pte_same(huge_ptep_get(ptep), pte))) {
                /* Break COW or unshare */
                huge_ptep_clear_flush(vma, haddr, ptep);
@@ -6397,7 +6392,7 @@ struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
                return NULL;
 
        hugetlb_vma_lock_read(vma);
-       pte = huge_pte_offset(mm, haddr, huge_page_size(h));
+       pte = hugetlb_walk(vma, haddr, huge_page_size(h));
        if (!pte)
                goto out_unlock;
 
@@ -6462,8 +6457,8 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 *
                 * Note that page table lock is not held when pte is null.
                 */
-               pte = huge_pte_offset(mm, vaddr & huge_page_mask(h),
-                                     huge_page_size(h));
+               pte = hugetlb_walk(vma, vaddr & huge_page_mask(h),
+                                  huge_page_size(h));
                if (pte)
                        ptl = huge_pte_lock(h, mm, pte);
                absent = !pte || huge_pte_none(huge_ptep_get(pte));
@@ -6654,7 +6649,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
        last_addr_mask = hugetlb_mask_last_page(h);
        for (; address < end; address += psize) {
                spinlock_t *ptl;
-               ptep = huge_pte_offset(mm, address, psize);
+               ptep = hugetlb_walk(vma, address, psize);
                if (!ptep) {
                        if (!uffd_wp) {
                                address |= last_addr_mask;
@@ -7064,8 +7059,8 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
 
                saddr = page_table_shareable(svma, vma, addr, idx);
                if (saddr) {
-                       spte = huge_pte_offset(svma->vm_mm, saddr,
-                                              vma_mmu_pagesize(svma));
+                       spte = hugetlb_walk(svma, saddr,
+                                           vma_mmu_pagesize(svma));
                        if (spte) {
                                get_page(virt_to_page(spte));
                                break;
@@ -7377,7 +7372,7 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
        hugetlb_vma_lock_write(vma);
        i_mmap_lock_write(vma->vm_file->f_mapping);
        for (address = start; address < end; address += PUD_SIZE) {
-               ptep = huge_pte_offset(mm, address, sz);
+               ptep = hugetlb_walk(vma, address, sz);
                if (!ptep)
                        continue;
                ptl = huge_pte_lock(h, mm, ptep);

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 93e13fc17d3cbf402906497debc04041cec4d2d6..4e448cfbc6efa715ee9805caa980bc2fc15522bc 100644 (file)
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -168,9 +168,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
                /* The only possible mapping was handled on last iteration */
                if (pvmw->pte)
                        return not_found(pvmw);
-
-               /* when pud is not present, pte will be NULL */
-               pvmw->pte = huge_pte_offset(mm, pvmw->address, size);
+               /*
+                * All callers that get here will already hold the
+                * i_mmap_rwsem.  Therefore, no additional locks need to be
+                * taken before calling hugetlb_walk().
+                */
+               pvmw->pte = hugetlb_walk(vma, pvmw->address, size);
                if (!pvmw->pte)
                        return false;
 

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index d98564a7be57cbed7c921e5b32fe61b55cce225a..cb23f8a15c134af536b9464e425660aba3f5ea6d 100644 (file)
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -305,13 +305,11 @@ static int walk_hugetlb_range(unsigned long addr, unsigned long end,
        hugetlb_vma_lock_read(vma);
        do {
                next = hugetlb_entry_end(h, addr, end);
-               pte = huge_pte_offset(walk->mm, addr & hmask, sz);
-
+               pte = hugetlb_walk(vma, addr & hmask, sz);
                if (pte)
                        err = ops->hugetlb_entry(pte, hmask, addr, next, walk);
                else if (ops->pte_hole)
                        err = ops->pte_hole(addr, next, -1, walk);
-
                if (err)
                        break;
        } while (addr = next, addr != end);