[merged mm-stable] mm-page_table_check-skip-zero-pages.patch removed from -mm tree

[merged mm-stable] mm-page_table_check-skip-zero-pages.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/page_table_check: skip zero pages
has been removed from the -mm tree.  Its filename was
     mm-page_table_check-skip-zero-pages.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Zhiling Zou <roxy520tt@gmail.com>
Subject: mm/page_table_check: skip zero pages
Date: Tue, 21 Jul 2026 23:56:38 +0800

page_table_check_set() accounts pages by whether they are PageAnon().  The
shared zero page is a special page, not an ordinary file-backed page. 
Read faults on private anonymous mappings can install many read-only PTEs
that point at the zero page, but page_table_check currently accounts them
in file_map_count.

That lets an unprivileged process populate enough zero-page mappings to
overflow file_map_count and trip the BUG_ON() in page_table_check_set().

Skip zero pages in page_table_check accounting.  They do not need the
anonymous/file mapping conflict checks that page_table_check performs for
ordinary pages, and this keeps the existing counter size and page_ext
layout unchanged.

Link: https://lore.kernel.org/1f8848512d2e3ded944f8d595c29faee8fdaeab0.1784645969.git.roxy520tt@gmail.com
Fixes: df4e817b7108 ("mm: page table check")
Signed-off-by: Zhiling Zou <roxy520tt@gmail.com>
Signed-off-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Cc: Ye Liu <liuye@kylinos.cn>
Cc: <stable@vger.kernel.org>
---

 mm/page_table_check.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/page_table_check.c~mm-page_table_check-skip-zero-pages
+++ a/mm/page_table_check.c
@@ -67,7 +67,7 @@ static void page_table_check_clear(unsig
 	struct page *page;
 	bool anon;
 
-	if (!pfn_valid(pfn))
+	if (!pfn_valid(pfn) || is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
 		return;
 
 	page = pfn_to_page(pfn);
@@ -102,7 +102,7 @@ static void page_table_check_set(unsigne
 	struct page *page;
 	bool anon;
 
-	if (!pfn_valid(pfn))
+	if (!pfn_valid(pfn) || is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
 		return;
 
 	page = pfn_to_page(pfn);
_

Patches currently in -mm which might be from roxy520tt@gmail.com are