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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 B5236C433DB for ; Thu, 14 Jan 2021 11:47:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 837DA23A40 for ; Thu, 14 Jan 2021 11:47:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726497AbhANLrT (ORCPT ); Thu, 14 Jan 2021 06:47:19 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30979 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726150AbhANLrT (ORCPT ); Thu, 14 Jan 2021 06:47:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610624752; 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=/v3H4Y1dgMiWDMdKL4Cn+sCUriko+UGoLRQTZJENYkU=; b=MLo9eJU4yubqa4yhqWu3k6kYL7zefyi3Xv0OMAWVyUU38NAPhQ0x7+Y3MctYrEt/AuFmZg K/1J/QVukIPzB6gqiC45vYedr5YHFje2/xFIRrXgRp0hbevLqwW9i8V2Fuh5Yk+0lROPqD dS9kjbThKz1o2/SR7eru3O+DxQcKXMQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-15-FzKYKq9oPHK-pP_fkGxNxA-1; Thu, 14 Jan 2021 06:45:48 -0500 X-MC-Unique: FzKYKq9oPHK-pP_fkGxNxA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B489915722; Thu, 14 Jan 2021 11:45:46 +0000 (UTC) Received: from work-vm (ovpn-115-29.ams2.redhat.com [10.36.115.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7AEBB10016F4; Thu, 14 Jan 2021 11:45:36 +0000 (UTC) Date: Thu, 14 Jan 2021 11:45:33 +0000 From: "Dr. David Alan Gilbert" To: Cornelia Huck Cc: Christian Borntraeger , Ram Pai , Halil Pasic , Greg Kurz , pair@us.ibm.com, brijesh.singh@amd.com, kvm@vger.kernel.org, "Michael S. Tsirkin" , qemu-devel@nongnu.org, frankja@linux.ibm.com, david@redhat.com, mdroth@linux.vnet.ibm.com, David Gibson , thuth@redhat.com, Eduardo Habkost , Richard Henderson , qemu-s390x@nongnu.org, rth@twiddle.net, berrange@redhat.com, Marcelo Tosatti , qemu-ppc@nongnu.org, pbonzini@redhat.com Subject: Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration Message-ID: <20210114114533.GF2905@work-vm> References: <20210104134629.49997b53.pasic@linux.ibm.com> <20210104184026.GD4102@ram-ibm-com.ibm.com> <20210105115614.7daaadd6.pasic@linux.ibm.com> <20210105204125.GE4102@ram-ibm-com.ibm.com> <20210111175914.13adfa2e.cohuck@redhat.com> <20210113124226.GH2938@work-vm> <6e02e8d5-af4b-624b-1a12-d03b9d554a41@de.ibm.com> <20210114103643.GD2905@work-vm> <20210114120531.3c7f350e.cohuck@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210114120531.3c7f350e.cohuck@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org * Cornelia Huck (cohuck@redhat.com) wrote: > On Thu, 14 Jan 2021 11:52:11 +0100 > Christian Borntraeger wrote: > > > On 14.01.21 11:36, Dr. David Alan Gilbert wrote: > > > * Christian Borntraeger (borntraeger@de.ibm.com) wrote: > > >> > > >> > > >> On 13.01.21 13:42, Dr. David Alan Gilbert wrote: > > >>> * Cornelia Huck (cohuck@redhat.com) wrote: > > >>>> On Tue, 5 Jan 2021 12:41:25 -0800 > > >>>> Ram Pai wrote: > > >>>> > > >>>>> On Tue, Jan 05, 2021 at 11:56:14AM +0100, Halil Pasic wrote: > > >>>>>> On Mon, 4 Jan 2021 10:40:26 -0800 > > >>>>>> Ram Pai wrote: > > >>>> > > >>>>>>> The main difference between my proposal and the other proposal is... > > >>>>>>> > > >>>>>>> In my proposal the guest makes the compatibility decision and acts > > >>>>>>> accordingly. In the other proposal QEMU makes the compatibility > > >>>>>>> decision and acts accordingly. I argue that QEMU cannot make a good > > >>>>>>> compatibility decision, because it wont know in advance, if the guest > > >>>>>>> will or will-not switch-to-secure. > > >>>>>>> > > >>>>>> > > >>>>>> You have a point there when you say that QEMU does not know in advance, > > >>>>>> if the guest will or will-not switch-to-secure. I made that argument > > >>>>>> regarding VIRTIO_F_ACCESS_PLATFORM (iommu_platform) myself. My idea > > >>>>>> was to flip that property on demand when the conversion occurs. David > > >>>>>> explained to me that this is not possible for ppc, and that having the > > >>>>>> "securable-guest-memory" property (or whatever the name will be) > > >>>>>> specified is a strong indication, that the VM is intended to be used as > > >>>>>> a secure VM (thus it is OK to hurt the case where the guest does not > > >>>>>> try to transition). That argument applies here as well. > > >>>>> > > >>>>> As suggested by Cornelia Huck, what if QEMU disabled the > > >>>>> "securable-guest-memory" property if 'must-support-migrate' is enabled? > > >>>>> Offcourse; this has to be done with a big fat warning stating > > >>>>> "secure-guest-memory" feature is disabled on the machine. > > >>>>> Doing so, will continue to support guest that do not try to transition. > > >>>>> Guest that try to transition will fail and terminate themselves. > > >>>> > > >>>> Just to recap the s390x situation: > > >>>> > > >>>> - We currently offer a cpu feature that indicates secure execution to > > >>>> be available to the guest if the host supports it. > > >>>> - When we introduce the secure object, we still need to support > > >>>> previous configurations and continue to offer the cpu feature, even > > >>>> if the secure object is not specified. > > >>>> - As migration is currently not supported for secured guests, we add a > > >>>> blocker once the guest actually transitions. That means that > > >>>> transition fails if --only-migratable was specified on the command > > >>>> line. (Guests not transitioning will obviously not notice anything.) > > >>>> - With the secure object, we will already fail starting QEMU if > > >>>> --only-migratable was specified. > > >>>> > > >>>> My suggestion is now that we don't even offer the cpu feature if > > >>>> --only-migratable has been specified. For a guest that does not want to > > >>>> transition to secure mode, nothing changes; a guest that wants to > > >>>> transition to secure mode will notice that the feature is not available > > >>>> and fail appropriately (or ultimately, when the ultravisor call fails). > > >>>> We'd still fail starting QEMU for the secure object + --only-migratable > > >>>> combination. > > >>>> > > >>>> Does that make sense? > > >>> > > >>> It's a little unusual; I don't think we have any other cases where > > >>> --only-migratable changes the behaviour; I think it normally only stops > > >>> you doing something that would have made it unmigratable or causes > > >>> an operation that would make it unmigratable to fail. > > >> > > >> I would like to NOT block this feature with --only-migrateable. A guest > > >> can startup unprotected (and then is is migrateable). the migration blocker > > >> is really a dynamic aspect during runtime. > > > > > > But the point of --only-migratable is to turn things that would have > > > blocked migration into failures, so that a VM started with > > > --only-migratable is *always* migratable. > > > > Hmmm, fair enough. How do we do this with host-model? The constructed model > > would contain unpack, but then it will fail to startup? Or do we silently > > drop unpack in that case? Both variants do not feel completely right. > > Failing if you explicitly specified unpacked feels right, but failing > if you just used the host model feels odd. Removing unpack also is a > bit odd, but I think the better option if we want to do anything about > it at all. 'host-model' feels a bit special; but breaking the rule that only-migratable doesn't change behaviour is weird. Can you do host,-unpack to make that work explicitly? But hang on; why is 'unpack' the name of a secure guest facility - is it really a feature for secure guest or something else? Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK