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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E5320C433FE for ; Wed, 9 Dec 2020 13:26:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A6C2223340 for ; Wed, 9 Dec 2020 13:26:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732210AbgLIN0C (ORCPT ); Wed, 9 Dec 2020 08:26:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:38714 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732188AbgLIN0C (ORCPT ); Wed, 9 Dec 2020 08:26:02 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0167123101; Wed, 9 Dec 2020 13:25:21 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kmzT4-00HOUv-VX; Wed, 09 Dec 2020 13:25:19 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 09 Dec 2020 13:25:18 +0000 From: Marc Zyngier To: Catalin Marinas Cc: Steven Price , Peter Maydell , Haibo Xu , lkml - Kernel Mailing List , Juan Quintela , Richard Henderson , QEMU Developers , "Dr. David Alan Gilbert" , Thomas Gleixner , Will Deacon , kvmarm , arm-mail-list , Dave Martin Subject: Re: [PATCH v5 0/2] MTE support for KVM guest In-Reply-To: <20201209124443.GB13566@gaia> References: <46fd98a2-ee39-0086-9159-b38c406935ab@arm.com> <0d0eb6da6a11f76d10e532c157181985@kernel.org> <20201207163405.GD1526@gaia> <874kkx5thq.wl-maz@kernel.org> <20201208172143.GB13960@gaia> <7ff14490e253878d0735633b792e1ea9@kernel.org> <20201209124443.GB13566@gaia> User-Agent: Roundcube Webmail/1.4.9 Message-ID: X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: catalin.marinas@arm.com, steven.price@arm.com, peter.maydell@linaro.org, haibo.xu@linaro.org, linux-kernel@vger.kernel.org, quintela@redhat.com, richard.henderson@linaro.org, qemu-devel@nongnu.org, dgilbert@redhat.com, tglx@linutronix.de, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Dave.Martin@arm.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-12-09 12:44, Catalin Marinas wrote: > On Tue, Dec 08, 2020 at 06:21:12PM +0000, Marc Zyngier wrote: >> On 2020-12-08 17:21, Catalin Marinas wrote: >> > On Mon, Dec 07, 2020 at 07:03:13PM +0000, Marc Zyngier wrote: >> > > I wonder whether we will have to have something kernel side to >> > > dump/reload tags in a way that matches the patterns used by live >> > > migration. >> > >> > We have something related - ptrace dumps/resores the tags. Can the same >> > concept be expanded to a KVM ioctl? >> >> Yes, although I wonder whether we should integrate this deeply into >> the dirty-log mechanism: it would be really interesting to dump the >> tags at the point where the page is flagged as clean from a dirty-log >> point of view. As the page is dirtied, discard the saved tags. > > From the VMM perspective, the tags can be treated just like additional > (meta)data in a page. We'd only need the tags when copying over. It can > race with the VM dirtying the page (writing tags would dirty it) but I > don't think the current migration code cares about this. If dirtied, it > copies it again. > > The only downside I see is an extra syscall per page both on the origin > VMM and the destination one to dump/restore the tags. Is this a > performance issue? I'm not sure. Migrating VMs already has a massive overhead, so an extra syscall per page isn't terrifying. But that's the point where I admit not knowing enough about what the VMM expects, nor whether that matches what happens on other architectures that deal with per-page metadata. Would this syscall operate on the guest address space? Or on the VMM's own mapping? M. -- Jazz is not dead. It just smells funny...