mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page

On some architectures (like ARM64), it can support CONT-PTE/PMD size
hugetlb, which means it can support not only PMD/PUD size hugetlb (2M and
1G), but also CONT-PTE/PMD size(64K and 32M) if a 4K page size specified.

So when looking up a CONT-PTE size hugetlb page by follow_page(), it will
use pte_offset_map_lock() to get the pte entry lock for the CONT-PTE size
hugetlb in follow_page_pte().  However this pte entry lock is incorrect
for the CONT-PTE size hugetlb, since we should use huge_pte_lock() to get
the correct lock, which is mm->page_table_lock.

That means the pte entry of the CONT-PTE size hugetlb under current pte
lock is unstable in follow_page_pte(), we can continue to migrate or
poison the pte entry of the CONT-PTE size hugetlb, which can cause some
potential race issues, even though they are under the 'pte lock'.

For example, suppose thread A is trying to look up a CONT-PTE size hugetlb
page by move_pages() syscall under the lock, however antoher thread B can
migrate the CONT-PTE hugetlb page at the same time, which will cause
thread A to get an incorrect page, if thread A also wants to do page
migration, then data inconsistency error occurs.

Moreover we have the same issue for CONT-PMD size hugetlb in
follow_huge_pmd().

To fix above issues, rename the follow_huge_pmd() as follow_huge_pmd_pte()
to handle PMD and PTE level size hugetlb, which uses huge_pte_lock() to
get the correct pte entry lock to make the pte entry stable.

Mike said:

Support for CONT_PMD/_PTE was added with bb9dd3df8ee9 ("arm64: hugetlb:
refactor find_num_contig()").  Patch series "Support for contiguous pte
hugepages", v4.  However, I do not believe these code paths were
executed until migration support was added with 5480280d3f2d ("arm64/mm:
enable HugeTLB migration for contiguous bit HugeTLB pages") I would go
with 5480280d3f2d for the Fixes: targe.

Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.1662017562.git.baolin.wang@linux.alibaba.com
Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3ec981a0d8b3a5b37f5cbd632f618ab139b36f48..67c88b82fc32d4acd3f3c78accf4c42737a0995a 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -207,8 +207,8 @@ struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address,
 struct page *follow_huge_pd(struct vm_area_struct *vma,
                            unsigned long address, hugepd_t hpd,
                            int flags, int pdshift);
-struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-                               pmd_t *pmd, int flags);
+struct page *follow_huge_pmd_pte(struct vm_area_struct *vma, unsigned long address,
+                                int flags);
 struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address,
                                pud_t *pud, int flags);
 struct page *follow_huge_pgd(struct mm_struct *mm, unsigned long address,
@@ -312,8 +312,8 @@ static inline struct page *follow_huge_pd(struct vm_area_struct *vma,
        return NULL;
 }
 
-static inline struct page *follow_huge_pmd(struct mm_struct *mm,
-                               unsigned long address, pmd_t *pmd, int flags)
+static inline struct page *follow_huge_pmd_pte(struct vm_area_struct *vma,
+                               unsigned long address, int flags)
 {
        return NULL;
 }

diff --git a/mm/gup.c b/mm/gup.c
index 00926abb44263b72b09872405bcaa93f344ae41b..251cb6a10bc0d67def35caff446a072284ebd811 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -530,6 +530,18 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
        if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
                         (FOLL_PIN | FOLL_GET)))
                return ERR_PTR(-EINVAL);
+
+       /*
+        * Considering PTE level hugetlb, like continuous-PTE hugetlb on
+        * ARM64 architecture.
+        */
+       if (is_vm_hugetlb_page(vma)) {
+               page = follow_huge_pmd_pte(vma, address, flags);
+               if (page)
+                       return page;
+               return no_page_table(vma, flags);
+       }
+
 retry:
        if (unlikely(pmd_bad(*pmd)))
                return no_page_table(vma, flags);
@@ -662,7 +674,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
        if (pmd_none(pmdval))
                return no_page_table(vma, flags);
        if (pmd_huge(pmdval) && is_vm_hugetlb_page(vma)) {
-               page = follow_huge_pmd(mm, address, pmd, flags);
+               page = follow_huge_pmd_pte(vma, address, flags);
                if (page)
                        return page;
                return no_page_table(vma, flags);

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0bdfc7e1c933f59c8084f9b4288201450c3d90cb..9564bf817e6a8d92999d2653304abf406a3f96d2 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6946,12 +6946,13 @@ follow_huge_pd(struct vm_area_struct *vma,
 }
 
 struct page * __weak
-follow_huge_pmd(struct mm_struct *mm, unsigned long address,
-               pmd_t *pmd, int flags)
+follow_huge_pmd_pte(struct vm_area_struct *vma, unsigned long address, int flags)
 {
+       struct hstate *h = hstate_vma(vma);
+       struct mm_struct *mm = vma->vm_mm;
        struct page *page = NULL;
        spinlock_t *ptl;
-       pte_t pte;
+       pte_t *ptep, pte;
 
        /*
         * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via
@@ -6961,17 +6962,15 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
                return NULL;
 
 retry:
-       ptl = pmd_lockptr(mm, pmd);
-       spin_lock(ptl);
-       /*
-        * make sure that the address range covered by this pmd is not
-        * unmapped from other threads.
-        */
-       if (!pmd_huge(*pmd))
-               goto out;
-       pte = huge_ptep_get((pte_t *)pmd);
+       ptep = huge_pte_offset(mm, address, huge_page_size(h));
+       if (!ptep)
+               return NULL;
+
+       ptl = huge_pte_lock(h, mm, ptep);
+       pte = huge_ptep_get(ptep);
        if (pte_present(pte)) {
-               page = pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT);
+               page = pte_page(pte) +
+                       ((address & ~huge_page_mask(h)) >> PAGE_SHIFT);
                /*
                 * try_grab_page() should always succeed here, because: a) we
                 * hold the pmd (ptl) lock, and b) we've just checked that the
@@ -6987,7 +6986,7 @@ retry:
        } else {
                if (is_hugetlb_entry_migration(pte)) {
                        spin_unlock(ptl);
-                       __migration_entry_wait_huge((pte_t *)pmd, ptl);
+                       __migration_entry_wait_huge(ptep, ptl);
                        goto retry;
                }
                /*