madvise(MADV_DONTNEED) ends up calling zap_page_range() to clear 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.

Address issue by: - 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. When called via MADV_DONTNEED, this flag is not set and the vm_lock is not deleted. - mmu notification is removed from __unmap_hugepage_range to avoid duplication, and notification is added to the other calling routine (unmap_hugepage_range). - notification calls are updated in zap_page range to take into account the possibility of multiple vmas.

[1] https://lore.kernel.org/lkml/CAO4mrfdLMXsao9RF4fUE8-Wfde8xmjsKrTNMNC9wjUb6Ju... 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: stable@vger.kernel.org --- include/linux/mm.h | 3 +++ mm/hugetlb.c | 45 +++++++++++++++++++++++++++------------------ mm/memory.c | 21 +++++++++++++++------ 3 files changed, 45 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h index 8bbcccbc5565..b19d65c36d14 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3475,4 +3475,7 @@ madvise_set_anon_name(struct mm_struct *mm, unsigned long start, */ #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 */ diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 546df97c31e4..4699889f11e9 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5064,7 +5064,6 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct 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(struct mmu_gather *tlb, struct vm_area_struct 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(struct mmu_gather *tlb, struct vm_area_struct if (ref_page) break; } - mmu_notifier_invalidate_range_end(&range); tlb_end_vma(tlb, vma);

/* @@ -5199,32 +5190,50 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb, 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. + * When called via zap_page_range (MADV_DONTNEED), this is not the + * final unmap of the vma, and we do not want to delete the vma_lock. */ - __hugetlb_vma_unlock_write_free(vma); - - i_mmap_unlock_write(vma->vm_file->f_mapping); + 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(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); }

diff --git a/mm/memory.c b/mm/memory.c index f88c351aecd4..474c43156ecf 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1720,7 +1720,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt, { 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 +1753,24 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start, 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(end, 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 'start-end' not 'range.start-range.end' as range + * could have been expanded for pmd sharing. + */ + unmap_single_vma(&tlb, vma, start, end, 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); }