FAILED: patch "[PATCH] mm: migrate_device: fix pte_pfn/pte_dirty called on" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 63867c82d0c0c2d182016a32b1cc0103116b0ea5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026080539-supremacy-prong-8fa9@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 63867c82d0c0c2d182016a32b1cc0103116b0ea5 Mon Sep 17 00:00:00 2001
From: Kefeng Wang <[email protected]>
Date: Mon, 6 Jul 2026 19:19:58 +0800
Subject: [PATCH] mm: migrate_device: fix pte_pfn/pte_dirty called on
 non-present PTE

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/[email protected]
Link: https://lore.kernel.org/[email protected]
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 <[email protected]>
Reviewed-by: Balbir Singh <[email protected]>
Acked-by: Zi Yan <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 554754eb26ff..908d2d4ec43a 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -401,7 +401,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			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 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			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 */