From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0601E1A9F9E for ; Wed, 13 Aug 2025 11:14:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755083661; cv=none; b=KyfZoDoTDcK2YYVEzIbOOM2CO7LBYLvVXcXbLIodjUJbTLc/iX7RtIw2jUMF3OpuUn5BDoVI99/qSgw0vV+3PErMTUBWfAjB5Rf7Jv2zFVqubFJJ5s0NjPWG+WMExZPrTyFRtnSE2T+Bb7pCTV9/INDZJJsx2+vEI6hfTZkvJE8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755083661; c=relaxed/simple; bh=jJ8Z6o7SASBnxW1/g8l1fDZr1YOffQeae3dgbacleoQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=S94i2TUOlwJjYoUmZlSYYUfj6/jdUxwXCncCvS6Nzqkbg0KyDTnEURYdJgNRPkBq1elaGPQLCI/haYIGGdOHEkruB9wOrx5q91uuRrtilpldmmyh/hDAUSeU2ojmXORVP5ipsbQOonzhRijVJRdARGu8sBX4I8jl14fSWcV7CRM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=CEOLR16n; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CEOLR16n" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755083658; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yNVE6wsMC8x7hacYqMkArJqlP3u73DUjInfZebo80YI=; b=CEOLR16nXv4mgE6fBUEAJaRWek/R/JjWq9rf9IDDV1KSxcPUM0fXyxdMMw1VqWaGopK0CD pe3x6DWDkXm/DUZKSEhKg362crVYxHXn9/qNXISUX5GrynzXOwV3ErYfKBtNKDhf+LeXkm 4ets82YC404NkZ1Tt8GMVk+NEtqShrE= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-205-4Pp8IIsdO9WiKTWHKKqYIA-1; Wed, 13 Aug 2025 07:14:12 -0400 X-MC-Unique: 4Pp8IIsdO9WiKTWHKKqYIA-1 X-Mimecast-MFC-AGG-ID: 4Pp8IIsdO9WiKTWHKKqYIA_1755083650 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id F1FC61800291; Wed, 13 Aug 2025 11:14:09 +0000 (UTC) Received: from localhost (unknown [10.72.112.177]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0043630001A1; Wed, 13 Aug 2025 11:14:07 +0000 (UTC) Date: Wed, 13 Aug 2025 19:14:02 +0800 From: Baoquan He To: Andrey Konovalov Cc: linux-mm@kvack.org, ryabinin.a.a@gmail.com, glider@google.com, dvyukov@google.com, vincenzo.frascino@arm.com, akpm@linux-foundation.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, sj@kernel.org, lorenzo.stoakes@oracle.com, elver@google.com, snovitoll@gmail.com Subject: Re: [PATCH v2 00/12] mm/kasan: make kasan=on|off work for all three modes Message-ID: References: <20250812124941.69508-1-bhe@redhat.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-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 08/12/25 at 07:14pm, Andrey Konovalov wrote: > On Tue, Aug 12, 2025 at 6:57 PM Andrey Konovalov wrote: > > > > On Tue, Aug 12, 2025 at 2:49 PM Baoquan He wrote: > > > > > > Currently only hw_tags mode of kasan can be enabled or disabled with > > > kernel parameter kasan=on|off for built kernel. For kasan generic and > > > sw_tags mode, there's no way to disable them once kernel is built. > > > This is not convenient sometime, e.g in system kdump is configured. > > > When the 1st kernel has KASAN enabled and crash triggered to switch to > > > kdump kernel, the generic or sw_tags mode will cost much extra memory > > > for kasan shadow while in fact it's meaningless to have kasan in kdump > > > kernel. > > > > > > So this patchset moves the kasan=on|off out of hw_tags scope and into > > > common code to make it visible in generic and sw_tags mode too. Then we > > > can add kasan=off in kdump kernel to reduce the unneeded meomry cost for > > > kasan. > > > > Hi Baoquan, > > > > Could you clarify what are you trying to achieve by disabling > > Generic/SW_TAGS KASAN via command-line? Do you want not to see any > > KASAN reports produced? Or gain back the performance? > > > > Because for the no reports goal, it would be much easier to add a > > command-line parameter to silent the reports. > > > > And the performance goal can only be partially achieved, as you cannot > > remove the compiler instrumentation without rebuilding the kernel. > > (What are the boot times for KASAN_GENERIC=n vs KASAN_GENERIC=y + > > kasan=off vs KASAN_GENERIC=y btw?) > > Thanks a lot for checking this. > > Ah, you don't want the shadow memory for kdump, sorry, I somehow missed that. Yeah, for kdump kernel, the shadow is a heavy burden, and most importantly kasan is useless for kdump. We don't want to capture a kernel memory bug through kdump kernel running becuase kdump is a debugging mechanism. > > I'm not familiar with the internals of kdump, but would it be > possible/reasonable to teach kdump to ignore the KASAN shadow region? Yes, we can teach kdump to do that. Then people may hate those conditional check "if (is_kdump_kernel())" being added in kasan code. E.g even though we skip kasan_init(), we still need to check is_kdump_kernel() in kasan_populate_vmalloc(), right? Combined with the existing kasan_arch_is_ready(), it will make kasan code ugly. I planned to add kasan_enabled() via static key kasan_flag_enabled, then it can also easily remove kasan_arch_is_ready() cleanly.