The patch titled Subject: mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Baolin Wang baolin.wang@linux.alibaba.com Subject: mm/hugetlb: fix races when looking up a CONT-PTE/PMD size hugetlb page Date: Thu, 1 Sep 2022 18:41:31 +0800

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.

Link: https://lkml.kernel.org/r/635f43bdd85ac2615a58405da82b4d33c6e5eb05.166201756... Signed-off-by: Baolin Wang baolin.wang@linux.alibaba.com Suggested-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 ---

include/linux/hugetlb.h | 8 ++++---- mm/gup.c | 14 +++++++++++++- mm/hugetlb.c | 27 +++++++++++++-------------- 3 files changed, 30 insertions(+), 19 deletions(-)

--- a/include/linux/hugetlb.h~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page +++ a/include/linux/hugetlb.h @@ -207,8 +207,8 @@ struct page *follow_huge_addr(struct mm_ 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_p 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; } --- a/mm/gup.c~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page +++ a/mm/gup.c @@ -530,6 +530,18 @@ static struct page *follow_page_pte(stru 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(stru 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); --- a/mm/hugetlb.c~mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page +++ a/mm/hugetlb.c @@ -6944,12 +6944,13 @@ follow_huge_pd(struct vm_area_struct *vm }

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 @@ -6959,17 +6960,15 @@ follow_huge_pmd(struct mm_struct *mm, un 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 @@ -6985,7 +6984,7 @@ 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; } /* _

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

mm-hugetlb-fix-races-when-looking-up-a-cont-pte-pmd-size-hugetlb-page.patch mm-migrate-do-not-retry-10-times-for-the-subpages-of-fail-to-migrate-thp.patch mm-damon-validate-if-the-pmd-entry-is-present-before-accessing.patch mm-damon-replace-pmd_huge-with-pmd_trans_huge-for-thp.patch