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

["David Hildenbrand (Arm)" <david@kernel.org>]

From: Chris Mason <mason@kernel.org>

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@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
[ david: simplify description ]
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1d65c4f576f9c..0c6512b33db0e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2493,7 +2493,7 @@ static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
 static void zap_huge_pmd_folio(struct mm_struct *mm, struct vm_area_struct *vma,
 		pmd_t pmdval, struct folio *folio, bool is_present)
 {
-	const bool is_device_private = folio_is_device_private(folio);
+	const bool is_device_private = pmd_is_device_private_entry(pmdval);
 
 	if (folio_test_anon(folio)) {
 		add_mm_counter(mm, MM_ANONPAGES, -HPAGE_PMD_NR);

-- 
2.43.0