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Mon, 11 Jan 2021 19:58:33 +0000 (GMT) Received: from ram-ibm-com.ibm.com (unknown [9.163.29.145]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Mon, 11 Jan 2021 19:58:33 +0000 (GMT) Date: Mon, 11 Jan 2021 11:58:30 -0800 From: Ram Pai To: Cornelia Huck Message-ID: <20210111195830.GA23898@ram-ibm-com.ibm.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111175914.13adfa2e.cohuck@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 Subject: RE: [for-6.0 v5 11/13] spapr: PEF: prevent migration X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343, 18.0.737 definitions=2021-01-11_30:2021-01-11, 2021-01-11 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 mlxlogscore=999 impostorscore=0 malwarescore=0 adultscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101110105 Received-SPF: pass client-ip=148.163.158.5; envelope-from=linuxram@us.ibm.com; helo=mx0b-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, 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: , Reply-To: Ram Pai Cc: 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, Halil Pasic , borntraeger@de.ibm.com, David Gibson , thuth@redhat.com, Eduardo Habkost , Richard Henderson , Greg Kurz , dgilbert@redhat.com, qemu-s390x@nongnu.org, rth@twiddle.net, berrange@redhat.com, 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 Mon, Jan 11, 2021 at 05:59:14PM +0100, Cornelia Huck 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). On POWER, secure-execution is not **automatically** enabled even when the host supports it. The feature is enabled only if the secure-object is configured, and the host supports it. However the behavior proposed above will be consistent on POWER and on s390x, when '--only-migratable' is specified and 'secure-object' is NOT specified. So I am in agreement till now. > We'd still fail starting QEMU for the secure object + --only-migratable > combination. Why fail? Instead, print a warning and disable the secure-object; which will disable your cpu-feature. Guests that do not transition to secure, will continue to operate, and guests that transition to secure, will fail. RP