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Thu, 14 Jan 2021 10:28:47 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.19.194]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Jan 2021 10:28:47 +0000 (GMT) Subject: Re: [for-6.0 v5 11/13] spapr: PEF: prevent migration To: "Dr. David Alan Gilbert" , Cornelia Huck References: <20201217054736.GH310465@yekko.fritz.box> <20201217123842.51063918.cohuck@redhat.com> <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> From: Christian Borntraeger Message-ID: <6e02e8d5-af4b-624b-1a12-d03b9d554a41@de.ibm.com> Date: Thu, 14 Jan 2021 11:28:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210113124226.GH2938@work-vm> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343, 18.0.737 definitions=2021-01-14_03:2021-01-13, 2021-01-14 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 suspectscore=0 mlxscore=0 mlxlogscore=999 bulkscore=0 lowpriorityscore=0 phishscore=0 impostorscore=0 adultscore=0 priorityscore=1501 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101140054 Received-SPF: pass client-ip=148.163.158.5; envelope-from=borntraeger@de.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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, Marcelo Tosatti , brijesh.singh@amd.com, frankja@linux.ibm.com, kvm@vger.kernel.org, "Michael S. Tsirkin" , Richard Henderson , david@redhat.com, Ram Pai , Greg Kurz , Eduardo Habkost , qemu-devel@nongnu.org, Halil Pasic , qemu-s390x@nongnu.org, qemu-ppc@nongnu.org, pbonzini@redhat.com, thuth@redhat.com, berrange@redhat.com, rth@twiddle.net, mdroth@linux.vnet.ibm.com, David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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.