[PATCH 14/46] mm/huge_memory: fix zapping migration entries for device-private THPs

[David Hildenbrand (Arm)]

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 ]
Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 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 eda020dd6e33f..1b50cc2b35351 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 = !is_present && pmd_is_device_private_entry(pmdval);
 
 	/* Transfer young+dirty while the folio is still mapped. */
 	if (is_present && !folio_test_anon(folio)) {

-- 
2.43.0