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A missing marker therefore means the range was > zapped, e.g. via MADV_DONTNEED. This applies to anon and shmem VMAs. > > An anonymous THP is write-protected in place as a huge PMD, so a > full-PMD MADV_DONTNEED clears it to pmd_none -- a hole with no page table > -- and pagemap_scan_pte_hole() misses it. For a MAP_PRIVATE|MAP_ANON > mapping MADV_DONTNEED has fill-with-zeros semantics, so a write-tracking > checkpoint/migration tool (e.g. CRIU) treats the range as unchanged and > keeps its previous contents; after restore or live migration the process > reads stale data instead of zeroes -- data corruption. > > Report a hole in a non-hugetlb uffd-wp VMA as written, matching the > pte_none handling in pagemap_page_category(); the existing > PM_SCAN_WP_MATCHING path then arms it via uffd_wp_range(). > > hugetlb is excluded: pagemap_hugetlb_category() reports an empty hugetlb > entry (huge_pte_none) as not-written, unlike pagemap_page_category(), > which reports pte_none as written. pagemap_scan_pte_hole() fires for a > hugetlb slot only when it has no page table; keeping that not-written > matches how an allocated-but-empty hugetlb entry reads, so the hole and > the empty-entry cases agree within the VMA. > > Reported-by: Sashiko AI review > Closes: https://sashiko.dev/#/patchset/20260707151349.92143-1-kirill@shutemov.name > Fixes: 2bad466cc9d9 ("mm/uffd: UFFD_FEATURE_WP_UNPOPULATED") > Cc: Muhammad Usama Anjum > Cc: Peter Xu > Cc: stable@vger.kernel.org > Signed-off-by: Kiryl Shutsemau > Assisted-by: Claude:claude-fable-5 Tested-by: Muhammad Usama Anjum