[v2 03/16] fs/proc: use softleaf_has_pfn() in pagemap PMD walker

[Usama Arif <usama.arif@linux.dev>]

pagemap_pmd_range_thp() assumes that every non-present PMD is a
migration entry and unconditionally calls softleaf_to_page().  This
will crash on any non-present PMD type that does not encode a PFN,
such as the upcoming PMD-level swap entries.

Guard the page lookup with softleaf_has_pfn(), matching how
pte_to_pagemap_entry() already handles non-present PTEs.

Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Usama Arif <usama.arif@linux.dev>
---
 fs/proc/task_mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index d32408f7cd5e..1fb5acd88ad0 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2129,7 +2129,8 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned long addr,
 			flags |= PM_SOFT_DIRTY;
 		if (pmd_swp_uffd_wp(pmd))
 			flags |= PM_UFFD_WP;
-		page = softleaf_to_page(entry);
+		if (softleaf_has_pfn(entry))
+			page = softleaf_to_page(entry);
 	}
 
 	if (page) {
-- 
2.52.0