From nobody Mon Apr 6 10:45:03 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9F1F13CBE77; Thu, 19 Mar 2026 11:50:09 +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=1773921011; cv=none; b=N6WjyMw1SCLQ1ePizXTkT/WGr4ijppX0WB1azTpp6NyId470F5BKXIWRVg5MBpYVy0aD0ZDXP/X18/dLZPvB1jSOlg0eeHibPkkE4qenZXXm9XqJeF7fudEubbBKRSgR7XS4U+4J6PsHW/TRJOFY3RMlU+tFxbGsw2l5ivl7Q5A= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773921011; c=relaxed/simple; bh=1A19svTFNimiMX0p7MePOMchlMQE04htLe+BZ1KV7so=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=UnnEOTR10AtjdbpMIketAh/JGXSmZxooY7eGGm9eMEzlBcdI0ZtZT66s9tryQznKWyli0u3ZfOHjL/CQMBfPMs2lxOiyjD44lWs2nqfgevpWAQpbsEAI1ZT6NCdfwWb50V1UqFKwFDYe74XeMp4RmX1h9Sz0r65t8vwYp9esvtk= 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 E2FDC1BD0; Thu, 19 Mar 2026 04:50:02 -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 B3FE63F778; Thu, 19 Mar 2026 04:50:04 -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 1/3] vmalloc: add __GFP_SKIP_KASAN support Date: Thu, 19 Mar 2026 11:49:44 +0000 Message-ID: <20260319114952.3241359-2-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-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable For allocations that will be accessed only with match-all pointers (e.g., kernel stacks), setting tags is wasted work. If the caller already set __GFP_SKIP_KASAN, don=E2=80=99t skip zeroing the pages and don=E2=80=99t set KASAN_VMALLOC_PROT_NORMAL so kasan_unpoison_vmalloc() returns early without tagging. Before this patch, __GFP_SKIP_KASAN wasn't being used with vmalloc APIs. So it wasn't being checked. Now its being checked and acted upon. Other KASAN modes are unchanged because __GFP_SKIP_KASAN isn't defined there. This is a preparatory patch for optimizing kernel stack allocations. Signed-off-by: Muhammad Usama Anjum --- mm/vmalloc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index c607307c657a6..1baa602a0b9bb 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4041,7 +4041,10 @@ void *__vmalloc_node_range_noprof(unsigned long size= , unsigned long align, * kasan_unpoison_vmalloc(). */ if (pgprot_val(prot) =3D=3D pgprot_val(PAGE_KERNEL)) { - if (kasan_hw_tags_enabled()) { + bool skip_kasan =3D kasan_hw_tags_enabled() && + (gfp_mask & __GFP_SKIP_KASAN); + + if (kasan_hw_tags_enabled() && !skip_kasan) { /* * Modify protection bits to allow tagging. * This must be done before mapping. @@ -4057,7 +4060,8 @@ void *__vmalloc_node_range_noprof(unsigned long size,= unsigned long align, } =20 /* Take note that the mapping is PAGE_KERNEL. */ - kasan_flags |=3D KASAN_VMALLOC_PROT_NORMAL; + if (!skip_kasan) + kasan_flags |=3D KASAN_VMALLOC_PROT_NORMAL; } =20 /* Allocate physical pages and map them into vmalloc space. */ --=20 2.47.3 From nobody Mon Apr 6 10:45:03 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 From nobody Mon Apr 6 10:45:03 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 7665B3CAE87; Thu, 19 Mar 2026 11:50:18 +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=1773921020; cv=none; b=gV7/zgZ30UjwYVk9QMNIdV28uiZ2t0TsQLrJMkV2fgKLstrvl2Hifn+ukIOLgj06il/jsTBOohNtHVUymfV3Yf/zWyKrf+JTI0tpAKY99MknE4jh1ShyrOY17KSqP4jksaRf4Bt9ar73PMVY6l6vBNUe1iIXkdDNYlMKG+1fXMI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773921020; c=relaxed/simple; bh=32l9uZ1km9Cm9dK1noYY5hOOta1mVAr1AsU5fQzpEgo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=et7J7R+4VebYbylkl/0o7NfQWG4tRsKhv7sPEwQncthQ2JzNeQY/M9e0Tk7jh1tJ/Br2wob7yHM0OmwaqFNs+ABtNpFcEH3s4SXhSvEwsCd4iOmExs330hZqQdOAJ6oWJ7TxlFggNvCuYZIncl3FUXYP5h9PKGigrZH9qxdu7vs= 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 05AEE20E3; Thu, 19 Mar 2026 04:50:12 -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 C7B4A3F778; Thu, 19 Mar 2026 04:50:13 -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 3/3] mm: SKIP KASAN for page table allocations Date: Thu, 19 Mar 2026 11:49:46 +0000 Message-ID: <20260319114952.3241359-4-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" Page tables are always accessed via __va(phys) / phys_to_virt(phys). With a match-all tag in the pointer, MTE never checks memory tags on access. Therefore: KASAN HW tags are set during page table allocation but never checked during use. KASAN poisoning on free provides no value for these pages as well. Its pure overhead - both at allocation time and free time. Hence, skip the tag setting for all page tables. Signed-off-by: Muhammad Usama Anjum Reviewed-by: Ryan Roberts --- include/asm-generic/pgalloc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/asm-generic/pgalloc.h b/include/asm-generic/pgalloc.h index 57137d3ac1592..051aa1331051c 100644 --- a/include/asm-generic/pgalloc.h +++ b/include/asm-generic/pgalloc.h @@ -4,7 +4,7 @@ =20 #ifdef CONFIG_MMU =20 -#define GFP_PGTABLE_KERNEL (GFP_KERNEL | __GFP_ZERO) +#define GFP_PGTABLE_KERNEL (GFP_KERNEL | __GFP_ZERO | __GFP_SKIP_KASAN) #define GFP_PGTABLE_USER (GFP_PGTABLE_KERNEL | __GFP_ACCOUNT) =20 /** --=20 2.47.3