[PATCH v2 06/19] mm/pagewalk: Check pfnmap for folio_walk_start()

[Peter Xu <peterx@redhat.com>]

Teach folio_walk_start() to recognize special pmd/pud mappings, and fail
them properly as it means there's no folio backing them.

Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/pagewalk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index cd79fb3b89e5..12be5222d70e 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -753,7 +753,7 @@ struct folio *folio_walk_start(struct folio_walk *fw,
 		fw->pudp = pudp;
 		fw->pud = pud;
 
-		if (!pud_present(pud) || pud_devmap(pud)) {
+		if (!pud_present(pud) || pud_devmap(pud) || pud_special(pud)) {
 			spin_unlock(ptl);
 			goto not_found;
 		} else if (!pud_leaf(pud)) {
@@ -783,7 +783,7 @@ struct folio *folio_walk_start(struct folio_walk *fw,
 		fw->pmdp = pmdp;
 		fw->pmd = pmd;
 
-		if (pmd_none(pmd)) {
+		if (pmd_none(pmd) || pmd_special(pmd)) {
 			spin_unlock(ptl);
 			goto not_found;
 		} else if (!pmd_leaf(pmd)) {
-- 
2.45.0