From nobody Mon Apr 6 12:12:13 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 11D9C3CD8C5; Thu, 19 Mar 2026 11:50:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773921015; cv=none; b=SQYi3ds2E8xIVcGwnoa8e17LT8LZkZFpuN++eC7E1QsTubhik40/lnN1YZW/9EBrrTQqIr9HFNnW6nvoidwVNoUkzZxMDBkFGGVN5klgUACBo0Sc39CI/M9COVLO6Vlq9CT7hGcDduMta4gwbAL9nY61uNR0So6rka2yvikIr/k= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773921015; c=relaxed/simple; bh=VbJHDsgOUKafanpIO//j3se8TUFIElNcsQTywAb0pqI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=r2qY2qs5o+8E9ttuQhYGH+7Hv4XBZeOymU5ar3sGgyFrfMkBraC93pDRS9da/+IMhcHtASqxEO/fcNCnYXfvwrxtjbWRajWhUi39CGNaB2y/PZDu36l3S3asMasw+qbffRlW/MT9s5HLCz7c+h8L9j4K+Y6JwJd98D+zLpVJAOA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 74FB82050; Thu, 19 Mar 2026 04:50:07 -0700 (PDT) Received: from e142334-100.cambridge.arm.com (e142334-100.cambridge.arm.com [10.1.194.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 438E03F778; Thu, 19 Mar 2026 04:50:09 -0700 (PDT) From: Muhammad Usama Anjum To: Arnd Bergmann , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Kees Cook , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Catalin Marinas , Will Deacon , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Cc: Muhammad Usama Anjum Subject: [PATCH 2/3] fork: skip MTE tagging for kernel stacks Date: Thu, 19 Mar 2026 11:49:45 +0000 Message-ID: <20260319114952.3241359-3-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260319114952.3241359-1-usama.anjum@arm.com> References: <20260319114952.3241359-1-usama.anjum@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The stack pointer always uses the match-all tag, so MTE never checks tags on stack accesses. Tagging stack memory on every thread creation is pure overhead. - Pass __GFP_SKIP_KASAN in gfp_mask for vmalloc-backed stacks so the vmalloc path skips HW tag setup (see previous patch). - For the cached VMAP reuse path, skip kasan_unpoison_range() when HW tags are enabled since the memory will only be accessed through the match-all tagged SP. - For the normal page allocator path, pass __GFP_SKIP_KASAN directly to the page allocator. Signed-off-by: Muhammad Usama Anjum --- kernel/fork.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index bb0c2613a5604..2baf4db39b5a4 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -345,7 +345,8 @@ static int alloc_thread_stack_node(struct task_struct *= tsk, int node) } =20 /* Reset stack metadata. */ - kasan_unpoison_range(vm_area->addr, THREAD_SIZE); + if (!kasan_hw_tags_enabled()) + kasan_unpoison_range(vm_area->addr, THREAD_SIZE); =20 stack =3D kasan_reset_tag(vm_area->addr); =20 @@ -358,7 +359,7 @@ static int alloc_thread_stack_node(struct task_struct *= tsk, int node) } =20 stack =3D __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, - GFP_VMAP_STACK, + GFP_VMAP_STACK | __GFP_SKIP_KASAN, node, __builtin_return_address(0)); if (!stack) return -ENOMEM; @@ -410,7 +411,8 @@ static void thread_stack_delayed_free(struct task_struc= t *tsk) =20 static int alloc_thread_stack_node(struct task_struct *tsk, int node) { - struct page *page =3D alloc_pages_node(node, THREADINFO_GFP, + struct page *page =3D alloc_pages_node(node, + THREADINFO_GFP | __GFP_SKIP_KASAN, THREAD_SIZE_ORDER); =20 if (likely(page)) { --=20 2.47.3