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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 98735C433DB for ; Thu, 14 Jan 2021 14:11:53 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4348923A05 for ; Thu, 14 Jan 2021 14:11:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4348923A05 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:38308 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l03Ls-0006LR-FS for qemu-devel@archiver.kernel.org; Thu, 14 Jan 2021 09:11:52 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:60304) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l03F1-0006VC-KG for qemu-devel@nongnu.org; Thu, 14 Jan 2021 09:04:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:52926) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l03Ew-0000a4-VD for qemu-devel@nongnu.org; Thu, 14 Jan 2021 09:04:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610633082; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gTmzUx4XqAggyZApGiSYmY6PGlS/O4UhRM5c2tO4Ock=; b=AB0Vt/H3rU89hM7OkzbgFS4kWiEJfv9qQxuhI9aDHhsiVQH8yIgLVXB3clJgvEbFq625wv WGBItpBsDp6q7IIA7BzOu4hTY89rUSDJejvZb9kxpI6aPCX3RDA74+g+KAv787HYjHlLpX RkwsXopF9f5uqLNkHo/CPWV8W2Ossro= 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-411-ZkcUa2JkOBabFPSGeDElSg-1; Thu, 14 Jan 2021 09:04:38 -0500 X-MC-Unique: ZkcUa2JkOBabFPSGeDElSg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EFA57C73B9; Thu, 14 Jan 2021 14:04:35 +0000 (UTC) Received: from gondolin (ovpn-114-65.ams2.redhat.com [10.36.114.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id A6FB16F985; Thu, 14 Jan 2021 14:04:25 +0000 (UTC) Date: Thu, 14 Jan 2021 15:04:22 +0100 From: Cornelia Huck To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration Message-ID: <20210114150422.5f74ca41.cohuck@redhat.com> In-Reply-To: <20210114122048.GG1643043@redhat.com> References: <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> <20210114114533.GF2905@work-vm> <20210114122048.GG1643043@redhat.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Received-SPF: pass client-ip=216.205.24.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.248, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pair@us.ibm.com, brijesh.singh@amd.com, kvm@vger.kernel.org, "Michael S. Tsirkin" , Ram Pai , qemu-devel@nongnu.org, frankja@linux.ibm.com, david@redhat.com, mdroth@linux.vnet.ibm.com, Halil Pasic , Christian Borntraeger , rth@twiddle.net, thuth@redhat.com, Eduardo Habkost , Richard Henderson , "Dr. David Alan Gilbert" , Greg Kurz , qemu-s390x@nongnu.org, David Gibson , Marcelo Tosatti , qemu-ppc@nongnu.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 14 Jan 2021 12:20:48 +0000 Daniel P. Berrang=C3=A9 wrote: > On Thu, Jan 14, 2021 at 12:50:12PM +0100, Christian Borntraeger wrote: > >=20 > >=20 > > On 14.01.21 12:45, Dr. David Alan Gilbert wrote: =20 > > > * Cornelia Huck (cohuck@redhat.com) wrote: =20 > > >> On Thu, 14 Jan 2021 11:52:11 +0100 > > >> Christian Borntraeger wrote: > > >> =20 > > >>> On 14.01.21 11:36, Dr. David Alan Gilbert wrote: =20 > > >>>> * Christian Borntraeger (borntraeger@de.ibm.com) wrote: =20 > > >>>>> > > >>>>> > > >>>>> On 13.01.21 13:42, Dr. David Alan Gilbert wrote: =20 > > >>>>>> * Cornelia Huck (cohuck@redhat.com) wrote: =20 > > >>>>>>> On Tue, 5 Jan 2021 12:41:25 -0800 > > >>>>>>> Ram Pai wrote: > > >>>>>>> =20 > > >>>>>>>> On Tue, Jan 05, 2021 at 11:56:14AM +0100, Halil Pasic wrote: = =20 > > >>>>>>>>> On Mon, 4 Jan 2021 10:40:26 -0800 > > >>>>>>>>> Ram Pai wrote: =20 > > >>>>>>> =20 > > >>>>>>>>>> The main difference between my proposal and the other propos= al is... > > >>>>>>>>>> > > >>>>>>>>>> In my proposal the guest makes the compatibility decision = and acts > > >>>>>>>>>> accordingly. In the other proposal QEMU makes the compati= bility > > >>>>>>>>>> decision and acts accordingly. I argue that QEMU cannot ma= ke a good > > >>>>>>>>>> compatibility decision, because it wont know in advance, i= f the guest > > >>>>>>>>>> will or will-not switch-to-secure. > > >>>>>>>>>> =20 > > >>>>>>>>> > > >>>>>>>>> You have a point there when you say that QEMU does not know i= n advance, > > >>>>>>>>> if the guest will or will-not switch-to-secure. I made that a= rgument > > >>>>>>>>> regarding VIRTIO_F_ACCESS_PLATFORM (iommu_platform) myself. M= y idea > > >>>>>>>>> was to flip that property on demand when the conversion occur= s. David > > >>>>>>>>> explained to me that this is not possible for ppc, and that h= aving 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 d= oes not > > >>>>>>>>> try to transition). That argument applies here as well. = =20 > > >>>>>>>> > > >>>>>>>> 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 tr= ansition. > > >>>>>>>> Guest that try to transition will fail and terminate themselve= s. =20 > > >>>>>>> > > >>>>>>> Just to recap the s390x situation: > > >>>>>>> > > >>>>>>> - We currently offer a cpu feature that indicates secure execut= ion 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, w= e add a > > >>>>>>> blocker once the guest actually transitions. That means that > > >>>>>>> transition fails if --only-migratable was specified on the co= mmand > > >>>>>>> line. (Guests not transitioning will obviously not notice any= thing.) > > >>>>>>> - 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 a= vailable > > >>>>>>> and fail appropriately (or ultimately, when the ultravisor call= fails). > > >>>>>>> We'd still fail starting QEMU for the secure object + --only-mi= gratable > > >>>>>>> combination. > > >>>>>>> > > >>>>>>> Does that make sense? =20 > > >>>>>> > > >>>>>> It's a little unusual; I don't think we have any other cases whe= re > > >>>>>> --only-migratable changes the behaviour; I think it normally onl= y stops > > >>>>>> you doing something that would have made it unmigratable or caus= es > > >>>>>> an operation that would make it unmigratable to fail. =20 > > >>>>> > > >>>>> I would like to NOT block this feature with --only-migrateable. A= guest > > >>>>> can startup unprotected (and then is is migrateable). the migrati= on blocker > > >>>>> is really a dynamic aspect during runtime. =20 > > >>>> > > >>>> But the point of --only-migratable is to turn things that would ha= ve > > >>>> blocked migration into failures, so that a VM started with > > >>>> --only-migratable is *always* migratable. =20 > > >>> > > >>> Hmmm, fair enough. How do we do this with host-model? The construct= ed model > > >>> would contain unpack, but then it will fail to startup? Or do we si= lently=20 > > >>> drop unpack in that case? Both variants do not feel completely righ= t. =20 > > >> > > >> 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 abo= ut > > >> it at all. =20 > > >=20 > > > '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? =20 > >=20 > > I guess that should work. But it means that we need to add logic in lib= virt > > to disable unpack for host-passthru and host-model. Next problem is the= n, > > that a future version might implement migration of such guests, which m= eans > > that libvirt must then stop fencing unpack. =20 >=20 > The "host-model" is supposed to always be migratable, so we should > fence the feature there. >=20 > host-passthrough is "undefined" whether it is migratable - it may or may > not work, no guarantees made by libvirt. >=20 > Ultimately I think the problem is that there ought to be an explicit > config to enable the feature for s390, as there is for SEV, and will > also presumably be needed for ppc.=20 Yes, an explicit config is what we want; unfortunately, we have to deal with existing setups as well... The options I see are - leave things for existing setups as they are now (i.e. might become unmigratable when the guest transitions), and make sure we're doing the right thing with the new object - always make the unpack feature conflict with migration requirements; this is a guest-visible change The first option might be less hairy, all considered?