mm/migrate_device: fix cache flush when replacing huge zero PMD

migrate_vma_insert_huge_pmd_page() calls flush_cache_page() before
replacing an existing huge zero PMD.  However, the third argument to
flush_cache_page() is a PFN, while addr + HPAGE_PMD_SIZE is an end virtual
address.

More importantly, the mapping being invalidated is PMD-sized rather than
PAGE_SIZE-sized.  Flush the whole PMD range with flush_cache_range(),
matching other huge PMD invalidation paths.

There is no userspace-visible effect today.  The architectures that
currently enable ARCH_ENABLE_THP_MIGRATION use no-op implementations of
flush_cache_page()/flush_cache_range().  32-bit ARM has non-trivial
implementations, but does not enable ARCH_ENABLE_THP_MIGRATION.

So this appears to be a latent API misuse rather than a currently
observable bug, and I don't think a stable backport is necessary.

Link: https://lore.kernel.org/20260817060845.377800-2-sh_def@163.com
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Signed-off-by: Hui Su <sh_def@163.com>
Reviewed-by: Balbir Singh <balbirs@nvidia.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 9a34616..762c5ce 100644 (file)
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -882,7 +882,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
 
        if (flush) {
                pte_free(vma->vm_mm, pgtable);
-               flush_cache_page(vma, addr, addr + HPAGE_PMD_SIZE);
+               flush_cache_range(vma, addr, addr + HPAGE_PMD_SIZE);
                pmdp_invalidate(vma, addr, pmdp);
        } else {
                pgtable_trans_huge_deposit(vma->vm_mm, pmdp, pgtable);