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 EE76AC54E76 for ; Tue, 17 Jan 2023 17:08:35 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pHpR7-0006VW-RA; Tue, 17 Jan 2023 12:07:49 -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 1pHpR7-0006VN-6z for qemu-devel@nongnu.org; Tue, 17 Jan 2023 12:07:49 -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 1pHpR5-0004HZ-7v for qemu-devel@nongnu.org; Tue, 17 Jan 2023 12:07:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673975265; 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=zx3zKZFLOeTrJ4XYrt2hPvepxZ1+7gKs5QAOksY3UGw=; b=Cz6vFqdZTCkOq6ULreS0HbZG/uq35ijGCJX5BaYEyo1guJNjkGlQFUPgQsbNR+/UCphO0E aryo6wmpgoRZvhb8Pu2VV7Ffg/L0urMq79yxc/w9CPL6HrXiabhNWFamMsRAIBq//faWx3 MlRhCjSxJyWHTmdXcfSU/R7NvMmVpAM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-433-5us2cJ4DMAiwhWVCxoUkpw-1; Tue, 17 Jan 2023 12:02:24 -0500 X-MC-Unique: 5us2cJ4DMAiwhWVCxoUkpw-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 7AD8E1C29D65; Tue, 17 Jan 2023 16:59:35 +0000 (UTC) Received: from localhost (unknown [10.39.192.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B9481492B00; Tue, 17 Jan 2023 16:59:34 +0000 (UTC) From: Cornelia Huck To: "Dr. David Alan Gilbert" , Peter Maydell Cc: Thomas Huth , Laurent Vivier , qemu-arm@nongnu.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, Eric Auger , Juan Quintela , Gavin Shan Subject: Re: [PATCH v4 1/2] arm/kvm: add support for MTE In-Reply-To: Organization: Red Hat GmbH References: <20230111161317.52250-1-cohuck@redhat.com> <20230111161317.52250-2-cohuck@redhat.com> User-Agent: Notmuch/0.37 (https://notmuchmail.org) Date: Tue, 17 Jan 2023 17:59:32 +0100 Message-ID: <877cxl85cb.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=unavailable 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 Tue, Jan 17 2023, "Dr. David Alan Gilbert" wrote: > * Peter Maydell (peter.maydell@linaro.org) wrote: >> On Wed, 11 Jan 2023 at 16:13, Cornelia Huck wrote: >> > >> > Introduce a new cpu feature flag to control MTE support. To preserve >> > backwards compatibility for tcg, MTE will continue to be enabled as >> > long as tag memory has been provided. >> > >> > If MTE has been enabled, we need to disable migration, as we do not >> > yet have a way to migrate the tags as well. Therefore, MTE will stay >> > off with KVM unless requested explicitly. >> > >> > Signed-off-by: Cornelia Huck >> > --- >> > docs/system/arm/cpu-features.rst | 21 +++++ >> > hw/arm/virt.c | 2 +- >> > target/arm/cpu.c | 18 ++--- >> > target/arm/cpu.h | 1 + >> > target/arm/cpu64.c | 133 +++++++++++++++++++++++++++++++ >> > target/arm/internals.h | 1 + >> > target/arm/kvm64.c | 5 ++ >> > target/arm/kvm_arm.h | 12 +++ >> > target/arm/monitor.c | 1 + >> > 9 files changed, 181 insertions(+), 13 deletions(-) >> > >> > diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst >> > index 00c444042ff5..e278650c837e 100644 >> > --- a/docs/system/arm/cpu-features.rst >> > +++ b/docs/system/arm/cpu-features.rst >> > @@ -443,3 +443,24 @@ As with ``sve-default-vector-length``, if the default length is larger >> > than the maximum vector length enabled, the actual vector length will >> > be reduced. If this property is set to ``-1`` then the default vector >> > length is set to the maximum possible length. >> > + >> > +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. >> > + >> > +If not specified explicitly via ``on`` or ``off``, MTE will be available >> > +according to the following rules: >> > + >> > +* When TCG is used, MTE will be available iff tag memory is available; i.e. it >> > + preserves the behaviour prior to introduction of the feature. >> > + >> > +* When KVM is used, MTE will default to off, so that migration will not >> > + unintentionally be blocked. >> > + >> > +* Other accelerators currently don't support MTE. >> >> Minor nits for the documentation: >> we should expand out "if and only if" -- not everybody recognizes >> "iff", especially if they're not native English speakers or not >> mathematicians. >> >> Should we write specifically that in a future QEMU version KVM >> might change to defaulting to "on if available" when migration >> support is implemented? > > Please make sure if you do something like that, that the failure > is obious; 'on if available' gets messy for things like libvirt > and higher level tools detecting features that are available and > machines they can migrate to. I guess we can just keep the door open but decline walking through it if we fail to come up with a good solution...