From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id ADA52C87FCF for ; Wed, 13 Aug 2025 12:10:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=yNVE6wsMC8x7hacYqMkArJqlP3u73DUjInfZebo80YI=; b=XN2sZ3ITYAgTxH/hw3NK+Do8Yd 4v/xoDg8wnejJHuEXMwcOylv3GqvCSbEYqqgUfP+5rp1B3dBcjIRo2Z6/HINeD4gdECLTg9nhYQeo +Avu3t0JnTD3VX+1/Ii0HZSlNsRnkbCJtPWR2BPJbmxhAaWvbkVOtCOD2M4pRUkHzdXPkWzt85kcf 6r0+lpocDwvJ8RfwOT+uYOg0PtEF+ELCT7TVXhB7BV0cBx1+JDvm0MBT2xJWtD3AogP4k4gwG6PrU LcZ+Dxnw09nIYtIePdRDAJMUYqLioWxa5LVBMi96F589h8VDz0or+6odmqUI94GBhIzYu2jYY5qYt juA7xfAA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1umAJG-0000000DbfS-2XuP; Wed, 13 Aug 2025 12:10:26 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1um9Qv-0000000DUZw-17ua for kexec@lists.infradead.org; Wed, 13 Aug 2025 11:14:20 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755083656; 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=SFWjPF+Tjlp3BINEsgMlxN2V49RstL6FMutoHuMcB9O4JkVCQCLGQHAbN52vUiCA4g1xI2 M8Veq1wZKtfyCw6GjZ9Ot6XStzq0rPB7TVGiJPFDazo02yzzj/q+f+ZrDDgiz7UNcQeRAj Ibrf4xydlDek42i5O1UlI0VEe+iE3kc= 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> 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250813_041417_388801_7B137CE4 X-CRM114-Status: GOOD ( 29.35 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org 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.