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Tue, 9 Jun 2020 16:28:48 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C002711C050; Tue, 9 Jun 2020 16:28:47 +0000 (GMT) Received: from oc2783563651 (unknown [9.145.129.89]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 9 Jun 2020 16:28:47 +0000 (GMT) Date: Tue, 9 Jun 2020 18:28:39 +0200 From: Halil Pasic To: Claudio Imbrenda Subject: Re: [PATCH v2 1/1] virtio-ccw: auto-manage VIRTIO_F_IOMMU_PLATFORM if PV Message-ID: <20200609182839.7ac80938.pasic@linux.ibm.com> In-Reply-To: <20200609174747.4e300818@ibm-vm> References: <20200514221155.32079-1-pasic@linux.ibm.com> <20200520121507-mutt-send-email-mst@kernel.org> <20200606013217.2cffa3ed.pasic@linux.ibm.com> <20200608181428.3c6f127c.cohuck@redhat.com> <20200608190045.319dd68b.pasic@linux.ibm.com> <20200609084402.35d317ec.cohuck@redhat.com> <20200609114130.0ca9190b.pasic@linux.ibm.com> <20200609174747.4e300818@ibm-vm> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-06-09_09:2020-06-09, 2020-06-09 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 mlxscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 cotscore=-2147483648 spamscore=0 phishscore=0 clxscore=1015 adultscore=0 mlxlogscore=895 lowpriorityscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006090118 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pasic@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/09 11:42:10 X-ACL-Warn: Detected OS = Linux 3.x [generic] [fuzzy] X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, KHOP_DYNAMIC=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Thomas Huth , Boris Fiuczynski , Janosch Frank , Pierre Morel , "Michael S. Tsirkin" , Cornelia Huck , David Hildenbrand , qemu-devel@nongnu.org, Christian Borntraeger , qemu-s390x@nongnu.org, David Gibson , Viktor Mihajlovski , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 9 Jun 2020 17:47:47 +0200 Claudio Imbrenda wrote: > On Tue, 9 Jun 2020 11:41:30 +0200 > Halil Pasic wrote: > > [...] > > > I don't know. Janosch could answer that, but he is on vacation. Adding > > Claudio maybe he can answer. My understanding is, that while it might > > be possible, it is ugly at best. The ability to do a transition is > > indicated by a CPU model feature. Indicating the feature to the guest > > and then failing the transition sounds wrong to me. > > I agree. If the feature is advertised, then it has to work. I don't > think we even have an architected way to fail the transition for that > reason. > > What __could__ be done is to prevent qemu from even starting if an > incompatible device is specified together with PV. AFAIU, the "specified together with PV" is the problem here. Currently we don't "specify PV" but PV is just a capability that is managed by the CPU model (like so many other). I.e. the fact that the visualization environment is capable providing PV (unpack facility available), and the fact, that the end user didn't fence the unpack facility, does not mean, the user is dead set to use PV. My understanding is, that we want PV to just work, without having to put together a peculiar VM definition that says: this is going to be used as a PV VM. > > Another option is to disable PV at the qemu level if an incompatible > device is present. This will have the effect that trying to boot a > secure guest will fail mysteriously, which is IMHO also not too great. > This would contradict with if feature is advertised, then it has to work or? > do we really have that many incompatible devices? >