The patch titled Subject: hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing has been added to the -mm mm-hotfixes-unstable branch. Its filename is hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing.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: Mike Kravetz mike.kravetz@oracle.com Subject: hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing Date: Mon, 31 Oct 2022 15:34:40 -0700

madvise(MADV_DONTNEED) ends up calling zap_page_range() to clear the page tables associated with the address range. For hugetlb vmas, zap_page_range will call __unmap_hugepage_range_final. However, __unmap_hugepage_range_final assumes the passed vma is about to be removed and deletes the vma_lock to prevent pmd sharing as the vma is on the way out. In the case of madvise(MADV_DONTNEED) the vma remains, but the missing vma_lock prevents pmd sharing and could potentially lead to issues with truncation/fault races.

This issue was originally reported here [1] as a BUG triggered in page_try_dup_anon_rmap. Prior to the introduction of the hugetlb vma_lock, __unmap_hugepage_range_final cleared the VM_MAYSHARE flag to prevent pmd sharing. Subsequent faults on this vma were confused as VM_MAYSHARE indicates a sharable vma, but was not set so page_mapping was not set in new pages added to the page table. This resulted in pages that appeared anonymous in a VM_SHARED vma and triggered the BUG.

Create a new routine clear_hugetlb_page_range() that can be called from madvise(MADV_DONTNEED) for hugetlb vmas. It has the same setup as zap_page_range, but does not delete the vma_lock. Also, add a new zap flag ZAP_FLAG_UNMAP to indicate an unmap call from unmap_vmas(). This is used to indicate the 'final' unmapping of a vma. The routine __unmap_hugepage_range to take a notification_needed argument. This is used to prevent duplicate notifications.

[1] https://lore.kernel.org/lkml/CAO4mrfdLMXsao9RF4fUE8-Wfde8xmjsKrTNMNC9wjUb6Ju...

Link: https://lkml.kernel.org/r/20221031223440.285187-1-mike.kravetz@oracle.com Fixes: 90e7e7f5ef3f ("mm: enable MADV_DONTNEED for hugetlb mappings") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Reported-by: Wei Chen harperchen1110@gmail.com Cc: Axel Rasmussen axelrasmussen@google.com Cc: David Hildenbrand david@redhat.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Mina Almasry almasrymina@google.com Cc: Nadav Amit nadav.amit@gmail.com Cc: Naoya Horiguchi naoya.horiguchi@linux.dev Cc: Peter Xu peterx@redhat.com Cc: Rik van Riel riel@surriel.com Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/hugetlb.h | 7 +++ include/linux/mm.h | 3 + mm/hugetlb.c | 80 ++++++++++++++++++++++++++++---------- mm/memory.c | 18 +++++--- 4 files changed, 82 insertions(+), 26 deletions(-)

--- a/include/linux/hugetlb.h~hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing +++ a/include/linux/hugetlb.h @@ -156,6 +156,8 @@ long follow_hugetlb_page(struct mm_struc void unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long, struct page *, zap_flags_t); +void clear_hugetlb_page_range(struct vm_area_struct *vma, + unsigned long start, unsigned long end); void __unmap_hugepage_range_final(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long start, unsigned long end, @@ -460,6 +462,11 @@ static inline void __unmap_hugepage_rang BUG(); }

+static void __maybe_unused clear_hugetlb_page_range(struct vm_area_struct *vma, + unsigned long start, unsigned long end) +{ +} + static inline vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags) --- a/include/linux/mm.h~hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing +++ a/include/linux/mm.h @@ -3475,4 +3475,7 @@ madvise_set_anon_name(struct mm_struct * */ #define ZAP_FLAG_DROP_MARKER ((__force zap_flags_t) BIT(0))

+/* Set in unmap_vmas() to indicate an unmap call. Only used by hugetlb */ +#define ZAP_FLAG_UNMAP ((__force zap_flags_t) BIT(1)) + #endif /* _LINUX_MM_H */ --- a/mm/hugetlb.c~hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing +++ a/mm/hugetlb.c @@ -5064,7 +5064,6 @@ static void __unmap_hugepage_range(struc struct page *page; struct hstate *h = hstate_vma(vma); unsigned long sz = huge_page_size(h); - struct mmu_notifier_range range; unsigned long last_addr_mask; bool force_flush = false;

@@ -5079,13 +5078,6 @@ static void __unmap_hugepage_range(struc tlb_change_page_size(tlb, sz); tlb_start_vma(tlb, vma);

- /* - * If sharing possible, alert mmu notifiers of worst case. - */ - mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, mm, start, - end); - adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); - mmu_notifier_invalidate_range_start(&range); last_addr_mask = hugetlb_mask_last_page(h); address = start; for (; address < end; address += sz) { @@ -5174,7 +5166,6 @@ static void __unmap_hugepage_range(struc if (ref_page) break; } - mmu_notifier_invalidate_range_end(&range); tlb_end_vma(tlb, vma);

/* @@ -5194,37 +5185,86 @@ static void __unmap_hugepage_range(struc tlb_flush_mmu_tlbonly(tlb); }

-void __unmap_hugepage_range_final(struct mmu_gather *tlb, +static void __unmap_hugepage_range_locking(struct mmu_gather *tlb, struct vm_area_struct *vma, unsigned long start, unsigned long end, struct page *ref_page, zap_flags_t zap_flags) { + bool final = zap_flags & ZAP_FLAG_UNMAP; + hugetlb_vma_lock_write(vma); i_mmap_lock_write(vma->vm_file->f_mapping);

__unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags);

- /* - * Unlock and free the vma lock before releasing i_mmap_rwsem. When - * the vma_lock is freed, this makes the vma ineligible for pmd - * sharing. And, i_mmap_rwsem is required to set up pmd sharing. - * This is important as page tables for this unmapped range will - * be asynchrously deleted. If the page tables are shared, there - * will be issues when accessed by someone else. - */ - __hugetlb_vma_unlock_write_free(vma); + if (final) { + /* + * Unlock and free the vma lock before releasing i_mmap_rwsem. + * When the vma_lock is freed, this makes the vma ineligible + * for pmd sharing. And, i_mmap_rwsem is required to set up + * pmd sharing. This is important as page tables for this + * unmapped range will be asynchrously deleted. If the page + * tables are shared, there will be issues when accessed by + * someone else. + */ + __hugetlb_vma_unlock_write_free(vma); + i_mmap_unlock_write(vma->vm_file->f_mapping); + } else { + i_mmap_unlock_write(vma->vm_file->f_mapping); + hugetlb_vma_unlock_write(vma); + } +} + +void __unmap_hugepage_range_final(struct mmu_gather *tlb, + struct vm_area_struct *vma, unsigned long start, + unsigned long end, struct page *ref_page, + zap_flags_t zap_flags) +{ + __unmap_hugepage_range_locking(tlb, vma, start, end, ref_page, + zap_flags); +} + +#ifdef CONFIG_ADVISE_SYSCALLS +/* + * Similar setup as in zap_page_range(). madvise(MADV_DONTNEED) can not call + * zap_page_range for hugetlb vmas as __unmap_hugepage_range_final will delete + * the associated vma_lock. + */ +void clear_hugetlb_page_range(struct vm_area_struct *vma, unsigned long start, + unsigned long end) +{ + struct mmu_notifier_range range; + struct mmu_gather tlb; + + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, + start, end); + adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); + tlb_gather_mmu(&tlb, vma->vm_mm); + update_hiwater_rss(vma->vm_mm); + mmu_notifier_invalidate_range_start(&range);

- i_mmap_unlock_write(vma->vm_file->f_mapping); + __unmap_hugepage_range_locking(&tlb, vma, start, end, NULL, 0); + + mmu_notifier_invalidate_range_end(&range); + tlb_finish_mmu(&tlb); } +#endif

void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, unsigned long end, struct page *ref_page, zap_flags_t zap_flags) { + struct mmu_notifier_range range; struct mmu_gather tlb;

+ mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm, + start, end); + adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); tlb_gather_mmu(&tlb, vma->vm_mm); + __unmap_hugepage_range(&tlb, vma, start, end, ref_page, zap_flags); + + mmu_notifier_invalidate_range_end(&range); tlb_finish_mmu(&tlb); }

--- a/mm/memory.c~hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing +++ a/mm/memory.c @@ -1720,7 +1720,7 @@ void unmap_vmas(struct mmu_gather *tlb, { struct mmu_notifier_range range; struct zap_details details = { - .zap_flags = ZAP_FLAG_DROP_MARKER, + .zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP, /* Careful - we need to zap private pages too! */ .even_cows = true, }; @@ -1753,15 +1753,21 @@ void zap_page_range(struct vm_area_struc MA_STATE(mas, mt, vma->vm_end, vma->vm_end);

lru_add_drain(); - mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, - start, start + size); tlb_gather_mmu(&tlb, vma->vm_mm); update_hiwater_rss(vma->vm_mm); - mmu_notifier_invalidate_range_start(&range); do { - unmap_single_vma(&tlb, vma, start, range.end, NULL); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, + vma->vm_mm, + max(start, vma->vm_start), + min(start + size, vma->vm_end)); + if (is_vm_hugetlb_page(vma)) + adjust_range_if_pmd_sharing_possible(vma, + &range.start, + &range.end); + mmu_notifier_invalidate_range_start(&range); + unmap_single_vma(&tlb, vma, start, start + size, NULL); + mmu_notifier_invalidate_range_end(&range); } while ((vma = mas_find(&mas, end - 1)) != NULL); - mmu_notifier_invalidate_range_end(&range); tlb_finish_mmu(&tlb); }

_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

hugetlb-dont-delete-vma_lock-in-hugetlb-madv_dontneed-processing.patch hugetlb-simplify-hugetlb-handling-in-follow_page_mask.patch hugetlb-simplify-hugetlb-handling-in-follow_page_mask-v4.patch