+ userfaultfd-wait-on-source-pmd-during-uffdio_move.patch added to mm-hotfixes-unstable branch

+ userfaultfd-wait-on-source-pmd-during-uffdio_move.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: userfaultfd: wait on source PMD during UFFDIO_MOVE
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     userfaultfd-wait-on-source-pmd-during-uffdio_move.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-wait-on-source-pmd-during-uffdio_move.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Usama Arif <usama.arif@linux.dev>
Subject: userfaultfd: wait on source PMD during UFFDIO_MOVE
Date: Sun, 5 Jul 2026 06:12:31 -0700

move_pages_huge_pmd() snapshots src_pmdval under src_ptl, drops the lock,
and, for migration entries, waits with pmd_migration_entry_wait().

Passing &src_pmdval is wrong.  pmd_migration_entry_wait() must lock and
re-read the real page-table PMD; on split-PMD-lock kernels, a stack
address also resolves to the wrong lock.  softleaf_entry_wait_on_locked()
then waits without a folio reference, which is safe only while serialized
against migration-entry removal by the real PT lock.

Pass src_pmd, matching __handle_mm_fault() and hmm_vma_walk_pmd().

Link: https://lore.kernel.org/20260705131231.1499198-1-usama.arif@linux.dev
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=8
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Rik van Riel <riel@surriel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/huge_memory.c~userfaultfd-wait-on-source-pmd-during-uffdio_move
+++ a/mm/huge_memory.c
@@ -2774,7 +2774,7 @@ int move_pages_huge_pmd(struct mm_struct
 	if (!pmd_trans_huge(src_pmdval)) {
 		spin_unlock(src_ptl);
 		if (pmd_is_migration_entry(src_pmdval)) {
-			pmd_migration_entry_wait(mm, &src_pmdval);
+			pmd_migration_entry_wait(mm, src_pmd);
 			return -EAGAIN;
 		}
 		return -ENOENT;
_

Patches currently in -mm which might be from usama.arif@linux.dev are

userfaultfd-wait-on-source-pmd-during-uffdio_move.patch
mm-swap_state-remove-unnecessary-lru_add_drain-from-readahead.patch
mm-add-softleaf_to_pmd-and-convert-existing-callers.patch
mm-extract-mm_prepare_for_swap_entries-helper.patch
fs-proc-use-softleaf_has_pfn-in-pagemap-pmd-walker.patch
mm-huge_memory-move-softleaf_to_folio-inside-migration-branch.patch
mm-migrate_device-move-softleaf_to_folio-inside-device-private-branch.patch
mm-rename-arch_enable_thp_migration-to-arch_supports_pmd_softleaf.patch
mm-vmpressure-skip-tree=true-accounting-on-cgroup-v2.patch
mm-vmpressure-skip-tree=true-accounting-on-cgroup-v2-fix.patch
mm-vmpressure-move-v1-userspace-eventfd-code-into-memcontrol-v1c.patch
mm-migrate_device-pin-large-folios-before-splitting.patch
mm-migrate_device-pin-large-folios-before-splitting-fix.patch