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Kiryl Shutsemau (Meta)
07b4377bdb
PAGEMAP_SCAN reports an unpopulated pte differently depending on which
path serves the request. The PAGE_IS_WRITTEN fast path in
pagemap_scan_pmd_entry() reports a pte_none as written (and, under
PM_SCAN_WP_MATCHING, arms a marker); pagemap_page_category() returns 0 for
the same pte_none. A request that cannot take the fast path (an extra
category bit, category_anyof_mask or category_inverted) therefore reports
the pte as clean and skips arming it.
A range that was populated and then MADV_DONTNEED'd reads as written via
one mask and clean via another, and in the latter case is not re-armed for
the next round -- an incremental-dump consumer (e.g. CRIU) using a richer
mask drops the zapped range and stops tracking writes to it.
Report pte_none as written in pagemap_page_category() too. A pte_none
carries no uffd-wp marker, i.e. it is not write-protected -- the same
condition under which the present and swap cases already report
PAGE_IS_WRITTEN. The fast path applies no VMA test, so neither does this.
The hugetlb and fully-unpopulated-PMD (no page table) scans have no
PAGE_IS_WRITTEN fast path, so they do not exhibit the per-entry divergence
and are left unchanged.
Add a pagemap_ioctl selftest that populates a range, drops it with
MADV_DONTNEED, and checks that the fast path and the generic
(category_anyof_mask) path both report every page written.
Link: https://lore.kernel.org/[email protected]
Fixes: 12f6b01a0b ("fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag")
Signed-off-by: Kiryl Shutsemau <[email protected]>
Cc: Muhammad Usama Anjum <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Pedro Falcato <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Assisted-by: Claude:claude-fable-5
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>