From nobody Sun Apr 5 13:26:25 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 24A763FA5CD; Tue, 24 Mar 2026 13:26:53 +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=1774358817; cv=none; b=A3Hwc+AKakKC4UIzy9kgh9/NjPCEUe6idErN/cHrzcrBqS6vw1nMwD+YdC3iD2ZuHql2M+Zbas/lX6502PsSa4vxvDUCX7sJzxOoDdhNLpaZI4dGYoMppBRiMuh7oN3kjifZklj1PWoaFB1a1Qk/yKwbOCDPMkX7GSkRUC85V80= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774358817; c=relaxed/simple; bh=6NeQ5I/ff6UfPXauvKRLpzI5NjSjxiyGIQia/li5NEU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=oeHT3WMbE+VueT7OInNbvayYg0xmyNfTCXujbZgx8st0WA3G0uXk+s1qrrDwQB/xUyUXIVulgSyDNlQZ5ZwRAGJ7zGhflS1qKppPrY+sp5ax+IoouWqcKWxqCaUpa2zS+9e/R7m/xM2j+4vZdCtg7Jsxie5XoxQSfSEwBOcZYfs= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=qz9/LE2J; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="qz9/LE2J" 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 76496153B; Tue, 24 Mar 2026 06:26:47 -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 2EE9B3FAF5; Tue, 24 Mar 2026 06:26:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1774358813; bh=6NeQ5I/ff6UfPXauvKRLpzI5NjSjxiyGIQia/li5NEU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qz9/LE2JSIbVqazwJDD5xbnrNC8yrlPETODw0hoy5dMfyizDqY+VzFRYSDYSH/CKK /c9GnUSEMsxDYg+JwKJvfdE3F6zZf3HzVb5xugM3CNuCzTEyDWJOiPTXlZP3CT4dzm Fj5EDqeQR83LSB8bdK9Sen3d8QclJAhA7SuLh9v8= 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 v2 1/3] vmalloc: add __GFP_SKIP_KASAN support Date: Tue, 24 Mar 2026 13:26:27 +0000 Message-ID: <20260324132631.482520-2-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260324132631.482520-1-usama.anjum@arm.com> References: <20260324132631.482520-1-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 --- Changes since v1: - Simplify skip conditions based on the fact that __GFP_SKIP_KASAN is zero in non-hw-tags mode. - Add __GFP_SKIP_KASAN to GFP_VMALLOC_SUPPORTED list of flags --- mm/vmalloc.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index c607307c657a6..69ae205effb46 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -3939,7 +3939,7 @@ static void *__vmalloc_area_node(struct vm_struct *ar= ea, gfp_t gfp_mask, __GFP_NOFAIL | __GFP_ZERO |\ __GFP_NORETRY | __GFP_RETRY_MAYFAIL |\ GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\ - GFP_USER | __GFP_NOLOCKDEP) + GFP_USER | __GFP_NOLOCKDEP | __GFP_SKIP_KASAN) =20 static gfp_t vmalloc_fix_flags(gfp_t flags) { @@ -3980,6 +3980,8 @@ static gfp_t vmalloc_fix_flags(gfp_t flags) * * %__GFP_NOWARN can be used to suppress failure messages. * + * %__GFP_SKIP_KASAN can be used to skip poisoning + * * Can not be called from interrupt nor NMI contexts. * Return: the address of the area or %NULL on failure */ @@ -4041,7 +4043,9 @@ 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 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 +4061,8 @@ 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 Sun Apr 5 13:26:25 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C2AED3F99C9; Tue, 24 Mar 2026 13:26:58 +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=1774358821; cv=none; b=RQt8HHglZXw5wPSYYHfdrN/1eVUr+JnE+pkzLNttO4ncbtKpcGhHqI4juX02F+NEC7psB1DyCeGQA0VCF14Vw9BwZzDqgbBGfLUxXK6PDoD/v0gsaEzVcp0tqqTXoZj7B7E/5vq57W3jlUa4YyrCPhU4KcX7yk5IP+AygdNWiEA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774358821; c=relaxed/simple; bh=VhBd0SXQdStB06Ok11/K+KdOFOf0X6cWYTl++e9UdAc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=AQhHHTwiBOBsb7/JRAjA2LQazKwUKrguP9PaqTCZe8An/rt517uC2ckMiBkm1nGxhJFL8Zn+Ec52kqYJBLaU0ao871tXkG9mq2Spd4oHjFElFt4oSmNYfhtcjnNb0X962MR40EHf7foB7PT6IRNiGH9dXsWEsOcX+MZgacNrpWg= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=Lay9mLSy; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="Lay9mLSy" 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 10331153B; Tue, 24 Mar 2026 06:26:52 -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 BD88D3FAF5; Tue, 24 Mar 2026 06:26:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1774358818; bh=VhBd0SXQdStB06Ok11/K+KdOFOf0X6cWYTl++e9UdAc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Lay9mLSy/mKrnA78g3qAMj48V6DZbVTZSKlQxfMcJT4P58/f6HDrxW5nnkZWA7i8v N4bdPcm3lyqUJky+4QOxQgv/m7/DvVhfe7M0UEBh86twBM/C8F7Ld4W4yjKhXniipe nOYfehEH0YKbdvhLs6jdw2/ti3BtLFWLvp1/FCCE= 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 v2 2/3] kasan: skip HW tagging for all kernel thread stacks Date: Tue, 24 Mar 2026 13:26:28 +0000 Message-ID: <20260324132631.482520-3-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260324132631.482520-1-usama.anjum@arm.com> References: <20260324132631.482520-1-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" HW-tag KASAN never checks kernel stacks because stack pointers carry the match-all tag, so setting/poisoning tags is pure overhead. - Add __GFP_SKIP_KASAN to THREADINFO_GFP so every stack allocator that uses it skips tagging (fork path plus arch users) - Add __GFP_SKIP_KASAN to GFP_VMAP_STACK for the fork-specific vmap stacks. - When reusing cached vmap stacks, skip kasan_unpoison_range() if HW tags are enabled. Software KASAN is unchanged; this only affects tag-based KASAN. Signed-off-by: Muhammad Usama Anjum --- Changes since v1: - Specify _GFP_SKIP_KASAN in THREADINFO_GFP and GFP_VMAP_STACK to use it everywhere and cover the missed locations - Update description --- include/linux/thread_info.h | 2 +- kernel/fork.c | 5 +++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 051e429026904..307b8390fc670 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -92,7 +92,7 @@ static inline long set_restart_fn(struct restart_block *r= estart, #define THREAD_ALIGN THREAD_SIZE #endif =20 -#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO) +#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_SKIP_KASA= N) =20 /* * flag set/clear/test wrappers diff --git a/kernel/fork.c b/kernel/fork.c index bb0c2613a5604..4bc7a03662109 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -207,7 +207,7 @@ static DEFINE_PER_CPU(struct vm_struct *, cached_stacks= [NR_CACHED_STACKS]); * accounting is performed by the code assigning/releasing stacks to tasks. * We need a zeroed memory without __GFP_ACCOUNT. */ -#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO) +#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO | __GFP_SKIP_KASAN) =20 struct vm_stack { struct rcu_head rcu; @@ -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 --=20 2.47.3 From nobody Sun Apr 5 13:26:25 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A0C283F9F40; Tue, 24 Mar 2026 13:27:03 +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=1774358826; cv=none; b=auP8tM91owHclwWfCT/e6VzzBOlhfU5ZFmC6keKIlgx796LFSX+ocub69Ik7wmobfjJHa7v7Sv7wWz5mp5b76NwblHs6Yw6l8LchAZ3f0xOlSEt/KFo/Sg7bRg7/OoW+4ipZV8M4G1nMplVqKDutJpTrQXGxLbL+f/OWG0mMblQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774358826; c=relaxed/simple; bh=Ia2GTAN1c3MwIjU4lUJMwHz1mGgU70Racq0g1YjJE6o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IDhDS71cEfYt0G8zkwOmQTmphJW/FGypWrSQFUvy117nGg85zap/xLpqFFWxW5P20HcZekmPgCPnUC0fsvxlKN9+PUvS5udoIRHJuMgZYfuzgTPM1DuT4f23uiGpLQL58PEXlkeEFbvvgEkieZyhmeENUjvn+XFyjpFKAwsRX1A= 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; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=s5ZzseGR; 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 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="s5ZzseGR" 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 C0CD6153B; Tue, 24 Mar 2026 06:26:56 -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 581333FAF5; Tue, 24 Mar 2026 06:26:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1774358822; bh=Ia2GTAN1c3MwIjU4lUJMwHz1mGgU70Racq0g1YjJE6o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=s5ZzseGRA1gs8qALby0g1l4GKGjy1Qp7cx+PS3+ynQOJDMP10D/yyoQ1OHvTRzkxt kjq/61LFc3TC089l2AvWmSO+0nEW0teFeCijTyp1NWeEfoW/1oZeJ9bAuVR0e8ivXY 51xIw/Q8egDHqIZ4MzLOzo4KaZq5vaffyPNhtCrw= 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 , Ryan Roberts Subject: [PATCH v2 3/3] mm: skip KASAN tagging for page-allocated page tables Date: Tue, 24 Mar 2026 13:26:29 +0000 Message-ID: <20260324132631.482520-4-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260324132631.482520-1-usama.anjum@arm.com> References: <20260324132631.482520-1-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 the linear mapping with a match-all tag, so HW-tag KASAN never checks them. For page-allocated tables (PTEs and PGDs etc), avoid the tag setup and poisoning overhead by using __GFP_SKIP_KASAN. SLUB-backed page tables are unchanged for now. (They aren't widely used and require more SLUB related skip logic. Leave it later.) Reviewed-by: Ryan Roberts Signed-off-by: Muhammad Usama Anjum --- Changes since v1: - Update description to mention SLUB-backed page tables are unchanged --- 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