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 1D833C433E0 for ; Thu, 14 Jan 2021 10:38:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E215F23A3B for ; Thu, 14 Jan 2021 10:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727326AbhANKi3 (ORCPT ); Thu, 14 Jan 2021 05:38:29 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:22894 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725954AbhANKi3 (ORCPT ); Thu, 14 Jan 2021 05:38:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610620623; 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=4ArMEYMxt1aGuAZDThGV6VJabcOkpJRR+nDUpyDI9Lk=; b=iQeagjFncLjWdDez2oUKygMJB1kWwci2LGzqelUvA9f/zxruusiOXF+/uXgM7Fq/cgMRoo uIt95bjdobMtmM08u5DaVldL0/kZjm1Scu5CuFlIkjno5y0eMy/1b1F5iUEL/6pJ/squUC L55iLMSgQxCe/WgzilPhCqwpm/a7QXc= 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-579-6igFpg3fPI2_xql-Ql6rXw-1; Thu, 14 Jan 2021 05:36:59 -0500 X-MC-Unique: 6igFpg3fPI2_xql-Ql6rXw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1E80B19251AE; Thu, 14 Jan 2021 10:36:57 +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 4136412D7E; Thu, 14 Jan 2021 10:36:45 +0000 (UTC) Date: Thu, 14 Jan 2021 10:36:43 +0000 From: "Dr. David Alan Gilbert" To: Christian Borntraeger Cc: Cornelia Huck , 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: <20210114103643.GD2905@work-vm> References: <20201217151530.54431f0e@bahia.lan> <20201218124111.4957eb50.cohuck@redhat.com> <20210104071550.GA22585@ram-ibm-com.ibm.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e02e8d5-af4b-624b-1a12-d03b9d554a41@de.ibm.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org * 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. Dave -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK