mm-mempolicy-skip-non-present-pmds-when-queueing-folios.patch removed from -mm tree

The quilt patch titled
Subject: mm/mempolicy: skip non-present PMDs when queueing folios
has been removed from the -mm tree. Its filename was
mm-mempolicy-skip-non-present-pmds-when-queueing-folios.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Usama Arif <[email protected]>
Subject: mm/mempolicy: skip non-present PMDs when queueing folios
Date: Fri, 10 Jul 2026 03:55:21 -0700

Patch series "mm: handle device-private PMDs in walk callbacks", v3.

Since commit 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations") a PMD may hold a device-private swap entry whenever an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages().

pmd_trans_huge_lock() succeeds for such PMDs (pmd_is_huge() returns true for any non-present, non-none huge PMD), so several MM walk callbacks that used to assume present THP or migration entry are now reachable with a device-private PMD. The results range from a VM_BUG_ON() firing on debug kernels, to an oops on a bogus vmemmap dereference, to silently isolating an unrelated live folio from LRU in the aliasing case.

This patch (of 3):

queue_folios_pmd() is called under pmd_trans_huge_lock(), whose pmd_is_huge() check returns true for any non-present, non-none PMD softleaf. Passing such a PMD to pmd_folio() treats the softleaf encoding as a hardware PFN and can return a bogus folio pointer.

Mirror queue_folios_pte_range(): handle non-present entries before looking up a folio. Keep migration entries counted as failures, but skip other non-present PMDs such as device-private entries.

Potential trigger: an HMM-based GPU driver migrates an anonymous THP folio to device memory via migrate_vma_pages(), leaving a device-private PMD. Userspace then calls mbind(), migrate_pages() or set_mempolicy_home_node() on that range.

---

 mm/mempolicy.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -654,12 +654,14 @@ static void queue_folios_pmd(pmd_t *pmd,
 {
 	struct folio *folio;
 	struct queue_pages *qp = walk->private;
+	pmd_t pmdval = pmdp_get(pmd);
 
-	if (unlikely(pmd_is_migration_entry(*pmd))) {
-		qp->nr_failed++;
+	if (unlikely(!pmd_present(pmdval))) {
+		if (pmd_is_migration_entry(pmdval))
+			qp->nr_failed++;
 		return;
 	}
-	folio = pmd_folio(*pmd);
+	folio = pmd_folio(pmdval);
 	if (is_huge_zero_folio(folio)) {
 		walk->action = ACTION_CONTINUE;
 		return;

_

Patches currently in -mm which might be from [email protected] are

mm-vmstat-mm-memcontrol-add-_monotonic-vmstat-readers.patch mm-vmscan-add-pgrotate_anon-and-pgrotate_file-vmstat-counters.patch mm-vmscan-reduce-lru_lock-contention-via-vmstat-derived-scan-balance-cost.patch