[PATCH v2 0/3] mm: reject zone device folios in more folio walkers

[Gregory Price]

Several LRU-oriented mm walkers resolve the folio backing a PMD entry
(or a physical pfn) and then reclaim, age, migrate, or lazyfree it
without ever checking for ZONE_DEVICE memory.

This series adds missing folio_is_zone_device() rejections, matching
the checks that comparable walkers already perform.

- mm/huge_memory, mm/madvise: the !pmd_present branch above these sites
  only filters device-private entries (which are non-present).

  A present zone device PMD (e.g. device-coherent) would still reach the
  folio and be lazyfreed / aged / paged out. Add an explicit check.

- mm/mempolicy: queue_folios_pmd() can see a present zone device PMD
  (e.g. device-coherent) and queue it for migration.

No crash reproducer - this is a correctness/hardening cleanup found by
inspection. All checks are placed after the folio is resolved and before
it is acted upon, on paths that already hold the relevant page-table lock,
so no locking or refcount changes are involved.

Gregory Price (3):
  mm/huge_memory: skip zone device folios in madvise_free_huge_pmd()
  mm/madvise: skip zone device folios in cold/pageout PMD range
  mm/mempolicy: skip zone device folios when queueing folios

 mm/huge_memory.c | 4 ++++
 mm/madvise.c     | 3 +++
 mm/mempolicy.c   | 2 ++
 3 files changed, 9 insertions(+)

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v2 - drop hugetlb, move checks earlier in queue migration route
   - fixes tags for all 3

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