bit means modified pages are missed, leading to inconsistent memory state after restore. As pointed out by David, the more critical uffd-wp bit is also dropped. This breaks the userfaultfd write-protection mechanism, causing writes to be silently missed by monitoring applications, which can lead to data corruption. Preserve both the soft-dirty and uffd-wp bits from the old PTE when creating the new zeropage mapping to ensure they are correctly tracked. Link: https://lkml.kernel.org/r/20250930081040.80926-1-lance.yang@linux.dev Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") Signed-off-by: Lance Yang Suggested-by: David Hildenbrand Suggested-by: Dev Jain Acked-by: David Hildenbrand Reviewed-by: Dev Jain Acked-by: Zi Yan Reviewed-by: Liam R. Howlett Reviewed-by: Harry Yoo Cc: Alistair Popple Cc: Baolin Wang Cc: Barry Song Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Jann Horn Cc: Joshua Hahn Cc: Lorenzo Stoakes Cc: Mariano Pache Cc: Mathew Brost Cc: Peter Xu Cc: Rakie Kim Cc: Rik van Riel Cc: Ryan Roberts Cc: Usama Arif Cc: Vlastimil Babka Cc: Yu Zhao Cc: Signed-off-by: Andrew Morton --- mm/migrate.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) --- a/mm/migrate.c~mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage +++ a/mm/migrate.c @@ -296,8 +296,7 @@ bool isolate_folio_to_list(struct folio } static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, - struct folio *folio, - unsigned long idx) + struct folio *folio, pte_t old_pte, unsigned long idx) { struct page *page = folio_page(folio, idx); pte_t newpte; @@ -306,7 +305,7 @@ static bool try_to_map_unused_to_zeropag return false; VM_BUG_ON_PAGE(!PageAnon(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); - VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page); + VM_BUG_ON_PAGE(pte_present(old_pte), page); if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) || mm_forbids_zeropage(pvmw->vma->vm_mm)) @@ -322,6 +321,12 @@ static bool try_to_map_unused_to_zeropag newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address), pvmw->vma->vm_page_prot)); + + if (pte_swp_soft_dirty(old_pte)) + newpte = pte_mksoft_dirty(newpte); + if (pte_swp_uffd_wp(old_pte)) + newpte = pte_mkuffd_wp(newpte); + set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte); dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio)); @@ -364,13 +369,13 @@ static bool remove_migration_pte(struct continue; } #endif + old_pte = ptep_get(pvmw.pte); if (rmap_walk_arg->map_unused_to_zeropage && - try_to_map_unused_to_zeropage(&pvmw, folio, idx)) + try_to_map_unused_to_zeropage(&pvmw, folio, old_pte, idx)) continue; folio_get(folio); pte = mk_pte(new, READ_ONCE(vma->vm_page_prot)); - old_pte = ptep_get(pvmw.pte); entry = pte_to_swp_entry(old_pte); if (!is_migration_entry_young(entry)) _ Patches currently in -mm which might be from lance.yang@linux.dev are hung_task-fix-warnings-caused-by-unaligned-lock-pointers.patch mm-khugepaged-abort-collapse-scan-on-non-swap-entries.patch[merged mm-hotfixes-stable] mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage.patch removed from -mm treeAndrew Morton undefinedmm-commits@vger.kernel.org,ziy@nvidia.com,yuzhao@google.com,ying.huang@linux.alibaba.com,vbabka@suse.cz,usamaarif642@gmail.com,stable@vger.kernel.org,ryan.roberts@arm.com,riel@surriel.com,rakie.kim@sk.com,peterx@redhat.com,npache@redhat.com,matthew.brost@intel.com,lorenzo.stoakes@oracle.com,Liam.Howlett@oracle.com,joshua.hahnjy@gmail.com,jannh@google.com,harry.yoo@oracle.com,gourry@gourry.net,dev.jain@arm.com,david@redhat.com,byungchul@sk.com,baolin.wang@linux.alibaba.com,baohua@kernel.org,apopple@nvidia.com,lance.yang@linux.dev,akpm@linux-foundation.org undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefinedınƒ†Y