Re: [PATCH v3] mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page

[Andrew Morton]

On Sat, 2 May 2026 10:59:33 +1000 Balbir Singh <balbirs@xxxxxxxxxx> wrote:

> > 
> > The issue can be reached if we try to migrate a non private/coherent folio (I assume DAX/P2PDMA)
> > pages. Even migrate_vma_insert_page() has a similar pattern. Creating the pud/pmd/pte structure
> > there is unnecessary (but not allocations occur, depends on pmd_none() for example), do we want
> > to clean up all of it (need to think through)?
> > 
> > I'll re-review and send fixes as needed. Looks like David sent some fixes out, will review
> > those as well.
> > 
> 
> I checked migrate_vma_insert_page() is no affected.
> 

Thanks.

What to do here.  We have a cc:stable hotfix which is adequately tested and
seems to have passed review.  And a cleanup patch from David.

I'm inclined to upstream this patch as-is and leave the cleanup on
David's TODO list (one more can't make any difference ;))

?


From: Sunny Patel <nueralspacetech@xxxxxxxxx>
Subject: mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page
Date: Fri, 1 May 2026 17:21:16 +0530

When migrate_vma_insert_huge_pmd_page() jumps to unlock_abort due
to a PMD check failure, the pgtable allocated earlier via
pte_alloc_one() is never freed, causing a memory leak.

Added free_abort label to release the pgtable in error path.

Link: https://lore.kernel.org/20260501115122.23288-1-nueralspacetech@xxxxxxxxx
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Signed-off-by: Sunny Patel <nueralspacetech@xxxxxxxxx>
Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
Reviewed-by: Huang Ying <ying.huang@xxxxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Balbir Singh <balbirs@xxxxxxxxxx>
Cc: Byungchul Park <byungchul@xxxxxx>
Cc: Gregory Price <gourry@xxxxxxxxxx>
Cc: Joshua Hahn <joshua.hahnjy@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Rakie Kim <rakie.kim@xxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/migrate_device.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/migrate_device.c~mm-migrate_device-fix-pgtable-leak-in-migrate_vma_insert_huge_pmd_page
+++ a/mm/migrate_device.c
@@ -840,7 +840,7 @@ static int migrate_vma_insert_huge_pmd_p
 	} else {
 		if (folio_is_zone_device(folio) &&
 		    !folio_is_device_coherent(folio)) {
-			goto abort;
+			goto free_abort;
 		}
 		entry = folio_mk_pmd(folio, vma->vm_page_prot);
 		if (vma->vm_flags & VM_WRITE)
@@ -893,6 +893,8 @@ static int migrate_vma_insert_huge_pmd_p
 
 unlock_abort:
 	spin_unlock(ptl);
+free_abort:
+	pte_free(vma->vm_mm, pgtable);
 abort:
 	for (i = 0; i < HPAGE_PMD_NR; i++)
 		src[i] &= ~MIGRATE_PFN_MIGRATE;
_