FAILED: patch "[PATCH] arm64: mte: Do not warn if the page is already tagged in" failed to apply to 6.12-stable tree

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

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 b98c94eed4a975e0c80b7e90a649a46967376f58
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025102649-rebirth-stray-74d8@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From b98c94eed4a975e0c80b7e90a649a46967376f58 Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Wed, 22 Oct 2025 11:09:14 +0100
Subject: [PATCH] arm64: mte: Do not warn if the page is already tagged in
 copy_highpage()

The arm64 copy_highpage() assumes that the destination page is newly
allocated and not MTE-tagged (PG_mte_tagged unset) and warns
accordingly. However, following commit 060913999d7a ("mm: migrate:
support poisoned recover from migrate folio"), folio_mc_copy() is called
before __folio_migrate_mapping(). If the latter fails (-EAGAIN), the
copy will be done again to the same destination page. Since
copy_highpage() already set the PG_mte_tagged flag, this second copy
will warn.

Replace the WARN_ON_ONCE(page already tagged) in the arm64
copy_highpage() with a comment.

Reported-by: syzbot+d1974fc28545a3e6218b@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/68dda1ae.a00a0220.102ee.0065.GAE@google.com
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: stable@vger.kernel.org # 6.12.x
Reviewed-by: Yang Shi <yang@os.amperecomputing.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/mm/copypage.c b/arch/arm64/mm/copypage.c
index a86c897017df..cd5912ba617b 100644
--- a/arch/arm64/mm/copypage.c
+++ b/arch/arm64/mm/copypage.c
@@ -35,7 +35,7 @@ void copy_highpage(struct page *to, struct page *from)
 		    from != folio_page(src, 0))
 			return;
 
-		WARN_ON_ONCE(!folio_try_hugetlb_mte_tagging(dst));
+		folio_try_hugetlb_mte_tagging(dst);
 
 		/*
 		 * Populate tags for all subpages.
@@ -51,8 +51,13 @@ void copy_highpage(struct page *to, struct page *from)
 		}
 		folio_set_hugetlb_mte_tagged(dst);
 	} else if (page_mte_tagged(from)) {
-		/* It's a new page, shouldn't have been tagged yet */
-		WARN_ON_ONCE(!try_page_mte_tagging(to));
+		/*
+		 * Most of the time it's a new page that shouldn't have been
+		 * tagged yet. However, folio migration can end up reusing the
+		 * same page without untagging it. Ignore the warning if the
+		 * page is already tagged.
+		 */
+		try_page_mte_tagging(to);
 
 		mte_copy_page_tags(kto, kfrom);
 		set_page_mte_tagged(to);