FAILED: patch "[PATCH] fs/proc: fix KPF_KSM reported for all anonymous pages" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 81401cebfc1598306b0a981b5f9ee5b58c1aac52
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072015-monkhood-mutation-c524@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 81401cebfc1598306b0a981b5f9ee5b58c1aac52 Mon Sep 17 00:00:00 2001
From: Jinjiang Tu <[email protected]>
Date: Fri, 26 Jun 2026 09:32:52 +0800
Subject: [PATCH] fs/proc: fix KPF_KSM reported for all anonymous pages

Reading /proc/kpageflags for any anonymous page returns KPF_KSM set, even when KSM is not in use. As a result, tools 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.

index f9b2c2c906cd..7d9387143435 100644
@@ -173,7 +173,7 @@ u64 stable_page_flags(const struct page *page)
 		u |= 1 << KPF_MMAP;
 	if (is_anon) {
 		u |= 1 << KPF_ANON;
-		if (mapping & FOLIO_MAPPING_KSM)
+		if ((mapping & FOLIO_MAPPING_FLAGS) == FOLIO_MAPPING_KSM)
 			u |= 1 << KPF_KSM;
 	}