[PATCH 6.18.y 2/3] mm/mempolicy: skip zone device folios when queueing folios

[Sasha Levin <sashal@kernel.org>]

From: Gregory Price <gourry@gourry.net>

[ Upstream commit 1f834ba9b42e3f3c298c7e8ef1df21b9947c92b4 ]

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).

Link: https://lore.kernel.org/20260817220810.1175596-4-gourry@gourry.net
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Balbir Singh <balbirs@nvidia.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
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: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Stable-dep-of: 9057170a941f ("mm/mempolicy: use vm_normal_folio_pmd() in queue_folios_pmd()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/mempolicy.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index adc52341c97cf..a6ee9526dc25e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -658,6 +658,8 @@ 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