From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 33E7234DCD2; Wed, 29 Apr 2026 14:43:36 +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=1777473817; cv=none; b=ikJU2+p0YtvkUAgUKhf280iLAh2J/sK28xXAfvgLKXnanoQBhvsqhj2NSVViOkwGIpqp0LTao6kX2HOHZyBHySJm7Y03DyDlVwTyqwYE8SL4pl10TY1EFrz9WdqvXTGH/oypVICDObhkXL96w0pLO0G/HJbx9ssPFrz0RErHl/k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777473817; c=relaxed/simple; bh=0QB+Qvxjjp0fPU4pPP754f+dTc32bLiJD+Cyf8FT9Y8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=GWOyeTP3eFfmVvv2eQRb5pOAYOKDXNM3eHL25FcRA6io2Nlo4EQ6AbSz35Mv6yKEy7Tbi3elkDYIudD26t63xaUGA6ZCPTsO/thJMD9uylkgjziwrH2MSOHmMOflcz6z7oighnRYV+IC38nm1hiuWw4s7eBEba0UqrTX23zJ138= 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=AgsKn4Dx; 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="AgsKn4Dx" 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 261911596; Wed, 29 Apr 2026 07:43:30 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7AB373F62B; Wed, 29 Apr 2026 07:43:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777473815; bh=0QB+Qvxjjp0fPU4pPP754f+dTc32bLiJD+Cyf8FT9Y8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AgsKn4Dxtc+zw54Fg3JARa6pKd6EWx9WJ4N4tIieLoiO0Yh9LcDjFwHvK/lNO6zbk 1NbhPkF0DRY2QP4bp1+HDQmSK21srsJJdMhaaHcvYnXNPCQ2C+uYwSBue7h1A8ZO1c HR4bYnQBmkZ5GexDoMfV0gabeltW9XYjiNMbL2/g= Date: Wed, 29 Apr 2026 15:43:23 +0100 From: Catalin Marinas To: Dev Jain Cc: akpm@linux-foundation.org, david@kernel.org, urezki@gmail.com, kees@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, arnd@arndb.de, Muhammad Usama Anjum , ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, tglx@kernel.org, mathieu.desnoyers@efficios.com, linux-arch@vger.kernel.org, ryan.roberts@arm.com Subject: Re: [PATCH v4 2/3] kasan: skip HW tagging for all kernel thread stacks Message-ID: References: <20260429102704.680174-1-dev.jain@arm.com> <20260429102704.680174-3-dev.jain@arm.com> Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260429102704.680174-3-dev.jain@arm.com> On Wed, Apr 29, 2026 at 03:57:03PM +0530, Dev Jain wrote: > From: Muhammad Usama Anjum > > 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 > Signed-off-by: Dev Jain Reviewed-by: Catalin Marinas