From 4165b7d1c45c2da0dfefe528f8d1fb7d79f0d344 Mon Sep 17 00:00:00 2001 From: Usama Arif Date: Sun, 5 Jul 2026 06:12:31 -0700 Subject: [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE 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 Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=8 Signed-off-by: Usama Arif Reviewed-by: Rik van Riel Reviewed-by: Baolin Wang Reviewed-by: Lance Yang Acked-by: David Hildenbrand (Arm) Reviewed-by: Lance Yang Reviewed-by: Lorenzo Stoakes Cc: Andrea Arcangeli Cc: Barry Song Cc: Dev Jain Cc: Johannes Weiner Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Shakeel Butt Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- 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 b5d1e9d4463d..032702a4637b 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2774,7 +2774,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm 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;