[5/6] mm: pagewalk: allow walk_page_range_novma() without mm

Commit Message

Rolf Eike Beer Aug. 22, 2022, 1:03 p.m. UTC

Since e47690d756a7 ("x86: mm: avoid allocating struct mm_struct on the
stack") a pgd can be passed to walk_page_range_novma(). In case it is set
no place in the pagewalk code use the walk.mm anymore, so permit to pass a
NULL mm instead. It is up to the caller to ensure proper locking on the pgd
in this case.

Signed-off-by: Rolf Eike Beer <[e-mail]>
---
 mm/pagewalk.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Patch

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index dc3c850cd148..f816f86588be 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -506,6 +506,8 @@  int walk_page_range(struct mm_struct *mm, unsigned long start,
  * not backed by VMAs. Because 'unusual' entries may be walked this function
  * will also not lock the PTEs for the pte_entry() callback. This is useful for
  * walking the kernel pages tables or page tables for firmware.
+ *
+ * Either mm or pgd may be NULL, but not both.
  */
 int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
 			  unsigned long end, const struct mm_walk_ops *ops,
@@ -520,10 +522,11 @@  int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
 		.no_vma		= true
 	};
 
-	if (start >= end || !walk.mm)
+	if (start >= end || (!walk.mm && !walk.pgd))
 		return -EINVAL;
 
-	mmap_assert_locked(walk.mm);
+	if (walk.mm)
+		mmap_assert_locked(walk.mm);
 
 	return walk_pgd_range(start, end, &walk);
 }