From eecd06034bf494f985cbcd1f062391d6a38f61c4 Mon Sep 17 00:00:00 2001
From: Usama Arif <usama.arif@linux.dev>
Date: Mon, 6 Jul 2026 04:42:05 -0700
Subject: [PATCH] fs/proc: use softleaf_has_pfn() in pagemap PMD walker

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.

Link: https://lore.kernel.org/20260706114320.1643046-4-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 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 229d1fc3d7f1..95012243b9b3 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) {