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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 4177EC6FA9D for ; Wed, 1 Mar 2023 14:15:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pXNF2-0005Ii-0G; Wed, 01 Mar 2023 09:15:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pXNEu-0005Gi-Cy for qemu-devel@nongnu.org; Wed, 01 Mar 2023 09:15:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pXNEr-0007e4-8g for qemu-devel@nongnu.org; Wed, 01 Mar 2023 09:15:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1677680124; 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: in-reply-to:in-reply-to:references:references; bh=KZK/Eir0iXKfCuBI/Twp952puaSpLfvrLp9JkJpn/ZA=; b=cIHAUQrArVB2DN2q4gQ47Di9DuiDZ+EP91JoWnfpqfoT+DNNIxhqmt+HpY0eKRogSflP4U WTOsnYf/7Zf4A6uhSFPiD6EurTjIrbbYXJsyBZjGC0MJiOMsS9YY8+rDm7zRkx/R5xuAAf eXhM4U/lfl0Aril0rMkvfW1dS6wZsww= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-659-x_3F7MgmPfq2-Z2EsiR_vg-1; Wed, 01 Mar 2023 09:15:20 -0500 X-MC-Unique: x_3F7MgmPfq2-Z2EsiR_vg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 842B5100F90F; Wed, 1 Mar 2023 14:15:19 +0000 (UTC) Received: from localhost (dhcp-192-239.str.redhat.com [10.33.192.239]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3D699492C3E; Wed, 1 Mar 2023 14:15:19 +0000 (UTC) From: Cornelia Huck To: Andrea Bolognani Cc: Peter Maydell , Thomas Huth , Laurent Vivier , qemu-arm@nongnu.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, Eric Auger , "Dr. David Alan Gilbert" , Juan Quintela , Gavin Shan , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Richard Henderson Subject: Re: [PATCH v6 1/2] arm/kvm: add support for MTE In-Reply-To: Organization: Red Hat GmbH References: <20230228150216.77912-1-cohuck@redhat.com> <20230228150216.77912-2-cohuck@redhat.com> <874jr4dbcr.fsf@redhat.com> User-Agent: Notmuch/0.37 (https://notmuchmail.org) Date: Wed, 01 Mar 2023 15:15:17 +0100 Message-ID: <87sfeoblsa.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Mar 01 2023, Andrea Bolognani wrote: > On Wed, Mar 01, 2023 at 11:17:40AM +0100, Cornelia Huck wrote: >> On Tue, Feb 28 2023, Andrea Bolognani wrote: >> > On Tue, Feb 28, 2023 at 04:02:15PM +0100, Cornelia Huck wrote: >> >> +MTE CPU Property >> >> +================ >> >> + >> >> +The ``mte`` property controls the Memory Tagging Extension. For TCG, it requires >> >> +presence of tag memory (which can be turned on for the ``virt`` machine via >> >> +``mte=on``). For KVM, it requires the ``KVM_CAP_ARM_MTE`` capability; until >> >> +proper migration support is implemented, enabling MTE will install a migration >> >> +blocker. >> > >> > Is it okay to use -machine virt,mte=on unconditionally for both KVM >> > and TCG guests when MTE support is requested, or will that not work >> > for the former? >> >> QEMU will error out if you try this with KVM (basically, same behaviour >> as before.) Is that a problem for libvirt, or merely a bit inconvinient? > > I'm actually a bit confused. The documentation for the mte property > of the virt machine type says > > mte > Set on/off to enable/disable emulating a guest CPU which implements > the Arm Memory Tagging Extensions. The default is off. > > So why is there a need to have a CPU property in addition to the > existing machine type property? I think the state prior to my patches is actually a bit confusing: the user needs to set a machine type property (causing tag memory to be allocated), which in turn enables a cpu feature. Supporting the machine type property for KVM does not make much sense IMHO: we don't allocate tag memory for KVM (in fact, that would not work). We have to keep the previous behaviour, and explicitly instructing QEMU to create cpus with a certain feature via a cpu property makes the most sense to me. We might want to tweak the documentation for the machine property to indicate that it creates tag memory and only implicitly enables mte but is a pre-req for it -- thoughts? > > From the libvirt integration point of view, setting the machine type > property only for TCG is not a problem. Ok.