+ mm-migrate_device-fix-pte_pfn-pte_dirty-called-on-non-present-pte.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-migrate_device-fix-pte_pfn-pte_dirty-called-on-non-present-pte.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate_device-fix-pte_pfn-pte_dirty-called-on-non-present-pte.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: Kefeng Wang <wangkefeng.wang@huawei.com>
Subject: mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE
Date: Mon, 6 Jul 2026 19:19:58 +0800

pte_pfn() and pte_dirty() have undefined behaviour when called on a
non-present PTE. In migrate_vma_collect_pmd(), these functions may be
invoked on non-present entries (e.g., device-private entries), leading
to potential crashes from pte_pfn() or incorrect dirty folio accounting
from pte_dirty(). Fix both by guarding with pte_present() checks.

Link: https://lore.kernel.org/20260708003955.4024340-1-wangkefeng.wang@huawei.com
Link: https://lore.kernel.org/20260706111958.3649651-1-wangkefeng.wang@huawei.com
Fixes: fd35ca3d12cc ("mm/migrate_device.c: copy pte dirty bit to page")
Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Balbir Singh <balbirs@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate_device.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/migrate_device.c~mm-migrate_device-fix-pte_pfn-pte_dirty-called-on-non-present-pte
+++ a/mm/migrate_device.c
@@ -401,7 +401,8 @@ again:
 			bool anon_exclusive;
 			pte_t swp_pte;
 
-			flush_cache_page(vma, addr, pte_pfn(pte));
+			if (pte_present(pte))
+				flush_cache_page(vma, addr, pte_pfn(pte));
 			anon_exclusive = folio_test_anon(folio) &&
 					  PageAnonExclusive(page);
 			if (anon_exclusive) {
@@ -422,7 +423,7 @@ again:
 			migrate->cpages++;
 
 			/* Set the dirty flag on the folio now the pte is gone. */
-			if (pte_dirty(pte))
+			if (pte_present(pte) && pte_dirty(pte))
 				folio_mark_dirty(folio);
 
 			/* Setup special migration page table entry */
_

Patches currently in -mm which might be from wangkefeng.wang@huawei.com are

mm-migrate_device-fix-pte_pfn-pte_dirty-called-on-non-present-pte.patch
mm-remove-pagetranscompound.patch
mm-mincore-use-walk_page_range_vma-in-do_mincore.patch
mm-mprotect-use-walk_page_range_vma-in-mprotect_fixup.patch
mm-mlock-use-walk_page_range_vma-in-mlock_vma_pages_range.patch
mm-migrate_device-use-walk_page_range_vma-in-migrate_vma_collect.patch