+ fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages.patch added to mm-hotfixes-unstable branch

+ fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: fs/proc: fix KPF_KSM reported for all anonymous pages
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jinjiang Tu <tujinjiang@huawei.com>
Subject: fs/proc: fix KPF_KSM reported for all anonymous pages
Date: Mon, 22 Jun 2026 17:15:39 +0800

Reading /proc/kpageflags for any anonymous page returns KPF_KSM set, even
when KSM is not in use.  As a result, tools which use /proc/kpageflags
(and hwpoison inject on a weird testing interface) misclassify all
anonymous pages as KSM merged.

In stable_page_flags(), if the page is anonymous, then use (mapping &
FOLIO_MAPPING_KSM) check to identify if the anonymous page is KSM page. 
However, FOLIO_MAPPING_KSM is FOLIO_MAPPING_ANON | FOLIO_MAPPING_ANON_KSM,
(mapping & FOLIO_MAPPING_KSM) check returns true for all anonymous pages.

To fix it, use FOLIO_MAPPING_ANON_KSM instead.

Link: https://lore.kernel.org/20260622091539.836531-1-tujinjiang@huawei.com
Fixes: dee3d0bef2b0 ("proc: rewrite stable_page_flags()")
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Luiz Capitulino <luizcap@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Svetly Todorov <svetly.todorov@memverge.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/page.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/proc/page.c~fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages
+++ a/fs/proc/page.c
@@ -173,7 +173,7 @@ u64 stable_page_flags(const struct page
 		u |= 1 << KPF_MMAP;
 	if (is_anon) {
 		u |= 1 << KPF_ANON;
-		if (mapping & FOLIO_MAPPING_KSM)
+		if (mapping & FOLIO_MAPPING_ANON_KSM)
 			u |= 1 << KPF_KSM;
 	}
 
_

Patches currently in -mm which might be from tujinjiang@huawei.com are

fs-proc-fix-kpf_ksm-reported-for-all-anonymous-pages.patch