Patch "mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page" has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

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

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8dc2ed7f7f38d46d077ebc92e20fcd8af49ca671
Author: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Date:   Thu Sep 1 18:41:31 2022 +0800

    mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page
    
    [ Upstream commit fac35ba763ed07ba93154c95ffc0c4a55023707f ]
    
    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@xxxxxxxxxxxxxxxxx
    Fixes: 5480280d3f2d ("arm64/mm: enable HugeTLB migration for contiguous bit HugeTLB pages")
    Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
    Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
    Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
    Cc: David Hildenbrand <david@xxxxxxxxxx>
    Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
    Cc: <stable@xxxxxxxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 22c1d935e22d..af8e7045017f 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -198,8 +198,8 @@ 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,
@@ -286,8 +286,8 @@ 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 1a23cd0b4fba..69e45cbe58f8 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -509,6 +509,18 @@ 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);
@@ -652,7 +664,7 @@ 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 f5f8929fad51..dbb63ec3b5fa 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6182,12 +6182,13 @@ 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_GET and FOLL_PIN are mutually exclusive. */
 	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
@@ -6195,17 +6196,15 @@ 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
@@ -6221,7 +6220,7 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
 	} else {
 		if (is_hugetlb_entry_migration(pte)) {
 			spin_unlock(ptl);
-			__migration_entry_wait(mm, (pte_t *)pmd, ptl);
+			__migration_entry_wait(mm, ptep, ptl);
 			goto retry;
 		}
 		/*



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