Re: [PATCH v3 3/3] mm/huge_memory: skip device-private PMDs in madvise_free_huge_pmd

[David Hildenbrand (Arm)]

On 7/10/26 12:55, Usama Arif wrote:
> madvise_free_pte_range() checks pmd_trans_huge(*pmd) unlocked, then
> madvise_free_huge_pmd() takes pmd_trans_huge_lock(). pmd_is_huge()
> returns true for a device-private PMD, so orig_pmd can be device-private
> and enter the !pmd_present() branch.
> 
> Skip device-private PMDs in that non-present branch and continue to out
> before calling pmd_folio(). Downgrade the check to VM_WARN_ON_ONCE() so
> an unexpected PMD softleaf logs a warning rather than panicking. Drop
> the thp_migration_supported() guard: it expands to
> IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_SOFTLEAF), and both
> pmd_is_migration_entry() and pmd_is_device_private_entry() already
> return false when that config is not selected, so the guard suppresses
> only the case where the warning would already be silent.
> 
> Potential trigger: an HMM-based GPU driver races with madvise(MADV_FREE):
> migrate_vma_pages() flips the PMD to a device-private entry between the
> caller's pmd_trans_huge() check and the callee's pmd_trans_huge_lock().
> 
> Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reviewed-by: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> Reviewed-by: Balbir Singh <balbirs@xxxxxxxxxx>
> Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
> ---

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David