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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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Usama Arif
2858b4027f
Patch series "mm: handle device-private PMDs in walk callbacks", v3. Since commit368076f52e("mm/huge_memory: add device-private THP support to PMD operations") a PMD may hold a device-private swap entry whenever an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages(). pmd_trans_huge_lock() succeeds for such PMDs (pmd_is_huge() returns true for any non-present, non-none huge PMD), so several MM walk callbacks that used to assume present THP or migration entry are now reachable with a device-private PMD. The results range from a VM_BUG_ON() firing on debug kernels, to an oops on a bogus vmemmap dereference, to silently isolating an unrelated live folio from LRU in the aliasing case. This patch (of 3): queue_folios_pmd() is called under pmd_trans_huge_lock(), whose pmd_is_huge() check returns true for any non-present, non-none PMD softleaf. Passing such a PMD to pmd_folio() treats the softleaf encoding as a hardware PFN and can return a bogus folio pointer. Mirror queue_folios_pte_range(): handle non-present entries before looking up a folio. Keep migration entries counted as failures, but skip other non-present PMDs such as device-private entries. Potential trigger: an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages(), leaving a device-private PMD. Userspace then calls mbind(), migrate_pages() or set_mempolicy_home_node() on that range. Link: https://lore.kernel.org/20260710105557.1987433-1-usama.arif@linux.dev Link: https://lore.kernel.org/20260710105557.1987433-2-usama.arif@linux.dev Fixes:368076f52e("mm/huge_memory: add device-private THP support to PMD operations") Signed-off-by: Usama Arif <usama.arif@linux.dev> Reported-by: sashiko-bot <sashiko-bot@kernel.org> Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6 Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Reviewed-by: Balbir Singh <balbirs@nvidia.com> Reviewed-by: Gregory Price <gourry@gourry.net> Cc: Alistair Popple <apopple@nvidia.com> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Byungchul Park <byungchul@sk.com> Cc: Dev Jain <dev.jain@arm.com> Cc: "Huang, Ying" <ying.huang@linux.alibaba.com> Cc: Jann Horn <jannh@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Lance Yang <lance.yang@linux.dev> Cc: Liam R. Howlett <liam@infradead.org> Cc: Lorenzo Stoakes <ljs@kernel.org> Cc: Matthew Brost <matthew.brost@intel.com> Cc: Nico Pache <npache@redhat.com> Cc: Rakie Kim <rakie.kim@sk.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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