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Commit65edfda6f3("mm/rmap: extend rmap and migration support device-private entries") introduced the concept of device-private PMD entries, but did not correctly update the rmap walk code to account for them. As a result, when page_vma_mapped_walk() encounters device-private PMD entries, it takes no action other than to acquire the PMD lock and exit. However this is highly problematic for two reasons - firstly, device private entries possess a PFN so check_pmd() needs to be called to ensure an overlapping PFN range. Secondly, and more importantly, if PVMW_MIGRATION is set the caller assumes the returned entry is a migration entry, resulting in memory corruption when the caller tries to interpret the device private entry as such. In addition, commit1462872900("mm/huge_memory: implement device-private THP splitting") allowed device private PMDs to be split like THP mappings, but again did not update this code path. As a result, we might race a PMD split prior to acquiring the PMD lock. This patch addresses all of these issues by invoking check_pmd(), ensuring PMVW_MIGRATION is not set and checks whether a split raced us we do for PMD THP and migration entries. Instead of checking for a subset of the cases after taking the pmd_lock(), put device-private along with pmd_trans_huge() and pmd_is_migration_entry(). Also remove thp_migration_supported() as it is already guarded by pmd_is_migration_entry(). [akpm@linux-foundation.org: fix Raspberry Pi 1 build, per David] Link: https://lore.kernel.org/20260630021540.17297-1-richard.weiyang@gmail.com Fixes:65edfda6f3("mm/rmap: extend rmap and migration support device-private entries") Signed-off-by: Wei Yang <richard.weiyang@gmail.com> Suggested-by: David Hildenbrand <david@kernel.org> Reviewed-by: Lance Yang <lance.yang@linux.dev> Acked-by: Balbir Singh <balbirs@nvidia.com> Tested-by: Klara Modin <klarasmodin@gmail.com> Cc: SeongJae Park <sj@kernel.org> Cc: Zi Yan <ziy@nvidia.com> Cc: Lorenzo Stoakes <ljs@kernel.org> Cc: <stable@vger.kernel.org>q Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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