FAILED: patch "[PATCH] mm/kfence: fix KASAN hardware tag faults during late" failed to apply to 6.1-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.1-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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x d155aab90fffa00f93cea1f107aef0a3d548b2ff
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026031730-shucking-dreaded-e3cf@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From d155aab90fffa00f93cea1f107aef0a3d548b2ff Mon Sep 17 00:00:00 2001
From: Alexander Potapenko <glider@google.com>
Date: Fri, 20 Feb 2026 15:49:40 +0100
Subject: [PATCH] mm/kfence: fix KASAN hardware tag faults during late
 enablement

When KASAN hardware tags are enabled, re-enabling KFENCE late (via
/sys/module/kfence/parameters/sample_interval) causes KASAN faults.

This happens because the KFENCE pool and metadata are allocated via the
page allocator, which tags the memory, while KFENCE continues to access it
using untagged pointers during initialization.

Use __GFP_SKIP_KASAN for late KFENCE pool and metadata allocations to
ensure the memory remains untagged, consistent with early allocations from
memblock.  To support this, add __GFP_SKIP_KASAN to the allowlist in
__alloc_contig_verify_gfp_mask().

Link: https://lkml.kernel.org/r/20260220144940.2779209-1-glider@google.com
Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
Signed-off-by: Alexander Potapenko <glider@google.com>
Suggested-by: Ernesto Martinez Garcia <ernesto.martinezgarcia@tugraz.at>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Marco Elver <elver@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index b5aedf505cec..7393957f9a20 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -1004,14 +1004,14 @@ static int kfence_init_late(void)
 #ifdef CONFIG_CONTIG_ALLOC
 	struct page *pages;
 
-	pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node,
-				   NULL);
+	pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL | __GFP_SKIP_KASAN,
+				   first_online_node, NULL);
 	if (!pages)
 		return -ENOMEM;
 
 	__kfence_pool = page_to_virt(pages);
-	pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node,
-				   NULL);
+	pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL | __GFP_SKIP_KASAN,
+				   first_online_node, NULL);
 	if (pages)
 		kfence_metadata_init = page_to_virt(pages);
 #else
@@ -1021,11 +1021,13 @@ static int kfence_init_late(void)
 		return -EINVAL;
 	}
 
-	__kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL);
+	__kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE,
+					  GFP_KERNEL | __GFP_SKIP_KASAN);
 	if (!__kfence_pool)
 		return -ENOMEM;
 
-	kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL);
+	kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE,
+						 GFP_KERNEL | __GFP_SKIP_KASAN);
 #endif
 
 	if (!kfence_metadata_init)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fcc32737f451..2d4b6f1a554e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6928,7 +6928,8 @@ static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
 {
 	const gfp_t reclaim_mask = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
 	const gfp_t action_mask = __GFP_COMP | __GFP_RETRY_MAYFAIL | __GFP_NOWARN |
-				  __GFP_ZERO | __GFP_ZEROTAGS | __GFP_SKIP_ZERO;
+				  __GFP_ZERO | __GFP_ZEROTAGS | __GFP_SKIP_ZERO |
+				  __GFP_SKIP_KASAN;
 	const gfp_t cc_action_mask = __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
 
 	/*