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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 6CC0CC4361B for ; Wed, 9 Dec 2020 12:45:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 19E9B23BC7 for ; Wed, 9 Dec 2020 12:45:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731833AbgLIMp3 (ORCPT ); Wed, 9 Dec 2020 07:45:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:50750 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731690AbgLIMp2 (ORCPT ); Wed, 9 Dec 2020 07:45:28 -0500 Date: Wed, 9 Dec 2020 12:44:43 +0000 From: Catalin Marinas To: Marc Zyngier 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 Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7ff14490e253878d0735633b792e1ea9@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? -- Catalin