Re: [PATCH] mm/huge_memory: fix override of entry in remove_migration_pmd
From: David Hildenbrand (Red Hat)
Date: Fri Nov 14 2025 - 04:23:10 EST
On 14.11.25 02:21, Balbir Singh wrote:
Recent changes exposed a BUG in remove_migration_pmd() where the
migration entry was being overridden when the folio is device private.
Use scope local entry for creating the device private pmde. Make the
pmde writable if the migration entry is writable by moving the check
is_migration_write() prior to creating the device private entry.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
Cc: Rakie Kim <rakie.kim@xxxxxx>
Cc: Byungchul Park <byungchul@xxxxxx>
Cc: Gregory Price <gourry@xxxxxxxxxx>
Cc: Ying Huang <ying.huang@xxxxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Cc: Nico Pache <npache@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Dev Jain <dev.jain@xxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Simona Vetter <simona@xxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Mika Penttilä <mpenttil@xxxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Francois Dugast <francois.dugast@xxxxxxxxx>
Signed-off-by: Balbir Singh <balbirs@xxxxxxxxxx>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
---
mm/huge_memory.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9dda8c48daca..df93768a6e15 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4698,7 +4698,12 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
folio_get(folio);
pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));
+ if (is_writable_migration_entry(entry))
+ pmde = pmd_mkwrite(pmde, vma);
+
if (folio_is_device_private(folio)) {
+ swp_entry_t entry;
+
if (pmd_write(pmde))
entry = make_writable_device_private_entry(
page_to_pfn(new));
@@ -4710,8 +4715,6 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
if (pmd_swp_soft_dirty(*pvmw->pmd))
pmde = pmd_mksoft_dirty(pmde);
- if (is_writable_migration_entry(entry))
- pmde = pmd_mkwrite(pmde, vma);
if (pmd_swp_uffd_wp(*pvmw->pmd))
pmde = pmd_mkuffd_wp(pmde);
if (!is_migration_entry_young(entry))
There are more problems here: you cannot call pmd_mksoft_dirty() etc on something that is not a present pmd! We have pmd_swp_mksoft_dirty() and friends for that.
So you'll have to completely split both paths.
--
Cheers
David