FAILED: patch "[PATCH] KVM: arm64: Omit tag sync on stage-2 mappings of the zero" 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 2986a625740599fe6e7635b0586fed2a95bcd1f7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026070242-concave-election-7ef2@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 2986a625740599fe6e7635b0586fed2a95bcd1f7 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <[email protected]>
Date: Thu, 4 Jun 2026 17:11:56 +0200
Subject: [PATCH] KVM: arm64: Omit tag sync on stage-2 mappings of the zero
page

Commit

f620d66af316 ("arm64: mte: Do not flag the zero page as PG_mte_tagged")

removed the PG_mte_tagged flag from the zero page, but missed a KVM code path that may set this flag on the zero page when it is used in a stage-2 CoW mapping of anonymous memory.

So disregard the zero page explicitly in sanitise_mte_tags().

index d089c107d9b7..445d6cf035c9 100644
@@ -1479,6 +1479,11 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
 	if (!kvm_has_mte(kvm))
 		return;
 
+	if (is_zero_pfn(pfn)) {
+		WARN_ON_ONCE(nr_pages != 1);
+		return;
+	}
+
 	if (folio_test_hugetlb(folio)) {
 		/* Hugetlb has MTE flags set on head page only */
 		if (folio_try_hugetlb_mte_tagging(folio)) {