Hi, Mike, Sorry to be late, took me quite some time working on another bug.. On Mon, Nov 07, 2022 at 05:19:09PM -0800, Mike Kravetz wrote: > 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-Wfde8xmjsKrTNMNC9wjUb6JudD0g@xxxxxxxxxxxxxx/ > Fixes: 90e7e7f5ef3f ("mm: enable MADV_DONTNEED for hugetlb mappings") > Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> > Reported-by: Wei Chen <harperchen1110@xxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > --- > 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)) It seems this is not set anywhere in the patch? > + > #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, Should this be s/UNMAP/CLEAR/? As IIUC the unmap path was only happening in __unmap_hugepage_range_final(). > + 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); I'd rather just call zap_page_range_single() directly with NULL passed over, considering that this is for stable, but no strong opinions. > 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 Same nitpick here, I'd rather keep the name at least for this patch. But again, no strong opinion. > * @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, > -- > 2.37.3 > > -- Peter Xu
