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[2620:137:e000::1:20]) by mx.google.com with ESMTP id ne17-20020a1709077b9100b0072b3b4f015csi11124692ejc.311.2022.07.11.08.09.19; Mon, 11 Jul 2022 08:09:19 -0700 (PDT) Received-SPF: pass (google.com: domain of kvm-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=XT9q6TV0; spf=pass (google.com: domain of kvm-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=kvm-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232059AbiGKPJJ (ORCPT + 2 others); Mon, 11 Jul 2022 11:09:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232070AbiGKPJG (ORCPT ); Mon, 11 Jul 2022 11:09:06 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 414465C97A for ; Mon, 11 Jul 2022 08:09:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1657552144; 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=kFM/HEtXZOYwhdUDHDICOY0NO6iZvyQ10TFIilDHEGc=; b=XT9q6TV0h7psBO01URMoMfLDTVlCpVDm/wisVAYGSP+BU23Cf8IxxJo/GKAyI31M74Le5B Olps4tUZ/iySF1vYxtZ3MhRjhoURv5Hk68Y7/PMatTpnUQvOBD1emmsMusjEXFVGlIjLGj Yp4lL8EKhRR5FbwJRZayULe+RE8zQ5g= 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-675-YLpegqmMNImf2jGbCwM8ZA-1; Mon, 11 Jul 2022 11:09:02 -0400 X-MC-Unique: YLpegqmMNImf2jGbCwM8ZA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5BE2F811E9B; Mon, 11 Jul 2022 15:09:01 +0000 (UTC) Received: from localhost (unknown [10.39.192.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 13C6440D296C; Mon, 11 Jul 2022 15:09:00 +0000 (UTC) From: Cornelia Huck To: "Dr. David Alan Gilbert" Cc: Peter Maydell , Thomas Huth , Laurent Vivier , Eric Auger , Juan Quintela , qemu-arm@nongnu.org, qemu-devel@nongnu.org, kvm@vger.kernel.org Subject: Re: [PATCH RFC v2 0/2] arm: enable MTE for QEMU + kvm In-Reply-To: Organization: Red Hat GmbH References: <20220707161656.41664-1-cohuck@redhat.com> User-Agent: Notmuch/0.36 (https://notmuchmail.org) Date: Mon, 11 Jul 2022 17:08:59 +0200 Message-ID: <87o7xv660k.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 on 10.11.54.2 X-Spam-Status: No, score=-3.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-TUID: AcCserUqAGUl On Mon, Jul 11 2022, "Dr. David Alan Gilbert" wrote: > * Cornelia Huck (cohuck@redhat.com) wrote: >> For kvm, mte stays off by default; this is because migration is not yet >> supported (postcopy will need an extension of the kernel interface, possibly >> an extension of the userfaultfd interface), and turning on mte will add a >> migration blocker. > > My assumption was that a normal migration would need something as well > to retrieve and place the MTE flags; albeit not atomically. There's KVM_ARM_MTE_COPY_TAGS, which should be sufficient to move tags around for normal migration. > >> My biggest question going forward is actually concerning migration; I gather >> that we should not bother adding something unless postcopy is working as well? > > I don't think that restriction is fair on you; just make sure > postcopy_ram_supported_by_host gains an arch call and fails cleanly; > that way if anyone tries to enable postcopy they'll find out with a > clean fail. Ok, if simply fencing off postcopy is fine, we can try to move forward with what we have now. The original attempt at https://lore.kernel.org/all/881871e8394fa18a656dfb105d42e6099335c721.1615972140.git.haibo.xu@linaro.org/ hooked itself directly into common code; maybe we should rather copy the approach used for s390 storage keys (extra "device") instead?