[PATCH v2 3/3] mm/mempolicy: skip zone device folios when queueing folios

[Gregory Price]

queue_folios_pte_range() already pairs vm_normal_folio() with an
explicit folio_is_zone_device() check before adding folios to the
migration pagelist.

vm_normal_folio() alone does not reject zone device memory (a present
device-coherent page in a normal VMA is returned as "normal").

Mirror the explicit check in queue_folios_pmd() as well.

queue_folios_pmd() uses pmd_folio() directly and can encounter a present
zone device PMD - e.g. a device-coherent THP.

This is not filtered by existing checks:
  !pmd_present()   - only rejects non-present device-private and
                     migration entries

  vma_migratable() - excludes DAX and VM_PFNMAP.

The early return also means such a folio is no longer counted in
qp->nr_failed under MPOL_MF_STRICT.  This is the same pattern used
by queue_folios_pte_range() (skipping zone device without failing).

Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 mm/mempolicy.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3498a5651d50f..3418b5664dcf8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -662,6 +662,8 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
 		return;
 	}
 	folio = pmd_folio(pmdval);
+	if (folio_is_zone_device(folio))
+		return;
 	if (is_huge_zero_folio(folio)) {
 		walk->action = ACTION_CONTINUE;
 		return;
-- 
2.53.0-Meta