Re: [PATCH v3 14/47] mm/huge_memory: fix zapping migration entries for device-private THPs

[Lance Yang]

On Sat, Oct 31, 2026 at 10:39:43AM +0100, David Hildenbrand (Arm) wrote:
>From: Chris Mason <mason@xxxxxxxxxx>
>
>A PMD migration entry can refer to a device-private folio.
>zap_huge_pmd_folio() checks the folio type instead of the entry type,
>so it treats such a migration entry as a device-private entry.
>
>Installing the migration entry already removed the reverse mapping and
>dropped the mapping reference. Zapping it must not repeat those
>operations. Concurrent MADV_DONTNEED during migration back to system
>memory can trigger this.
>
>Check the PMD entry type using pmd_is_device_private_entry().
>
>Fix generated by an LLM and sent by Chris Mason in private.
>
>Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations")
>Cc: stable@xxxxxxxxxxxxxxx
>Signed-off-by: Chris Mason <mason@xxxxxxxxxx>
>[ david: simplify description ]
>Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
>Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>---

Reviewed-by: Lance Yang <lance.yang@xxxxxxxxx>