[PATCH v6 36/39] mm: avoid use of VMA_SPECIAL_FLAGS in migrate_vma_setup()

[Lorenzo Stoakes (ARM)]

Now we have the expressive vma_is_mm_backed() predicate, use it to
determine whether to proceed with migration. This drops the VMA_IO_BIT
test, which is safe as mm-managed mappings may not set it.

hugetlb mappings are mm-backed but remain explicitly excluded, as the
migrate_vma page walk has no hugetlb support.

No functional change intended.

Reviewed-by: Zi Yan <ziy at nvidia.com>
Acked-by: David Hildenbrand (Arm) <david at kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs at kernel.org>
---
 mm/migrate_device.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index b9c453c28795..9e19fadfa65c 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -739,19 +739,21 @@ static void migrate_vma_unmap(struct migrate_vma *migrate)
  */
 int migrate_vma_setup(struct migrate_vma *args)
 {
+	const struct vm_area_struct *vma = args->vma;
 	long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
 
 	args->start &= PAGE_MASK;
 	args->end &= PAGE_MASK;
-	if (!args->vma || vma_test_any_mask(args->vma, VMA_SPECIAL_FLAGS) ||
-	    vma_is_dax(args->vma))
+	if (!vma)
+		return -EINVAL;
+	/* The migrate_vma page walk has no hugetlb support. */
+	if (!vma_is_mm_backed(vma) || vma_is_hugetlb(vma) || vma_is_dax(vma))
 		return -EINVAL;
 	if (nr_pages <= 0)
 		return -EINVAL;
-	if (args->start < args->vma->vm_start ||
-	    args->start >= args->vma->vm_end)
+	if (args->start < vma->vm_start || args->start >= vma->vm_end)
 		return -EINVAL;
-	if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
+	if (args->end <= vma->vm_start || args->end > vma->vm_end)
 		return -EINVAL;
 	if (!args->src || !args->dst)
 		return -EINVAL;

-- 
2.55.0