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 range in zap_page_range_single is updated to take into account the possibility of hugetlb pmd sharing. - zap_page_range_single renamed to __zap_page_range_single to be used internally within mm/memory.c - zap_vma_range() interface created to zap a range within a single vma. - madvise_dontneed_single_vma is updated to call zap_vma_range instead of zap_page_range as it only operates on a range within a single vma
[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 | 5 +++++ mm/hugetlb.c | 45 +++++++++++++++++++++++++++------------------ mm/madvise.c | 4 ++-- mm/memory.c | 17 +++++++++++++---- 4 files changed, 47 insertions(+), 24 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 978c17df053e..d205bcd9cd2e 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1840,6 +1840,8 @@ void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address, unsigned long size); void zap_page_range(struct vm_area_struct *vma, unsigned long address, unsigned long size); +void zap_vma_range(struct vm_area_struct *vma, unsigned long address, + unsigned long size); void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt, struct vm_area_struct *start_vma, unsigned long start, unsigned long end); @@ -3464,4 +3466,7 @@ 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 ceb47c4e183a..7c8fbce4441e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5072,7 +5072,6 @@ 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;
@@ -5087,13 +5086,6 @@ 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) { @@ -5178,7 +5170,6 @@ 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);
/* @@ -5203,32 +5194,50 @@ 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_vma_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/madvise.c b/mm/madvise.c index c7105ec6d08c..9d2625b8029a 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -772,7 +772,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma, * Application no longer needs these pages. If the pages are dirty, * it's OK to just throw them away. The app will be more careful about * data it wants to keep. Be sure to free swap resources too. The - * zap_page_range call sets things up for shrink_active_list to actually free + * zap_vma_range call sets things up for shrink_active_list to actually free * these pages later if no one else has touched them in the meantime, * although we could add these pages to a global reuse list for * shrink_active_list to pick up before reclaiming other pages. @@ -790,7 +790,7 @@ static int madvise_free_single_vma(struct vm_area_struct *vma, static long madvise_dontneed_single_vma(struct vm_area_struct *vma, unsigned long start, unsigned long end) { - zap_page_range(vma, start, end - start); + zap_vma_range(vma, start, end - start); return 0; }
diff --git a/mm/memory.c b/mm/memory.c index 6090124b64f1..af3a4724b464 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1717,7 +1717,7 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start, }
/** - * zap_page_range_single - remove user pages in a given range + * __zap_page_range_single - remove user pages in a given range * @vma: vm_area_struct holding the applicable pages * @address: starting address of pages to zap * @size: number of bytes to zap @@ -1725,7 +1725,7 @@ void zap_page_range(struct vm_area_struct *vma, unsigned long start, * * The range must fit into one VMA. */ -static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address, +static void __zap_page_range_single(struct vm_area_struct *vma, unsigned long address, unsigned long size, struct zap_details *details) { struct mmu_notifier_range range; @@ -1734,6 +1734,9 @@ static void zap_page_range_single(struct vm_area_struct *vma, unsigned long addr lru_add_drain(); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, address, address + size); + if (is_vm_hugetlb_page(vma)) + 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); @@ -1742,6 +1745,12 @@ static void zap_page_range_single(struct vm_area_struct *vma, unsigned long addr tlb_finish_mmu(&tlb); }
+void zap_vma_range(struct vm_area_struct *vma, unsigned long address, + unsigned long size) +{ + __zap_page_range_single(vma, address, size, NULL); +} + /** * zap_vma_ptes - remove ptes mapping the vma * @vma: vm_area_struct holding ptes to be zapped @@ -1760,7 +1769,7 @@ void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address, !(vma->vm_flags & VM_PFNMAP)) return;
- zap_page_range_single(vma, address, size, NULL); + __zap_page_range_single(vma, address, size, NULL); } EXPORT_SYMBOL_GPL(zap_vma_ptes);
@@ -3453,7 +3462,7 @@ static void unmap_mapping_range_vma(struct vm_area_struct *vma, unsigned long start_addr, unsigned long end_addr, struct zap_details *details) { - zap_page_range_single(vma, start_addr, end_addr - start_addr, details); + __zap_page_range_single(vma, start_addr, end_addr - start_addr, details); }
static inline void unmap_mapping_range_tree(struct rb_root_cached *root,