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Wed, 10 Jun 2020 13:01:02 +0000 (GMT) Received: from oc2783563651 (unknown [9.145.127.50]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 10 Jun 2020 13:01:02 +0000 (GMT) Date: Wed, 10 Jun 2020 15:00:33 +0200 From: Halil Pasic To: David Hildenbrand Subject: Re: [PATCH v2 1/1] virtio-ccw: auto-manage VIRTIO_F_IOMMU_PLATFORM if PV Message-ID: <20200610150033.5608ff95.pasic@linux.ibm.com> In-Reply-To: <858e9554-a4c7-6487-121b-ac3eaa209cb7@redhat.com> References: <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> <20200609182839.7ac80938.pasic@linux.ibm.com> <20200609124155-mutt-send-email-mst@kernel.org> <20200610043118.GF494336@umbus.fritz.box> <4e5d62d8-9bfb-67d5-7398-2079729fd85e@redhat.com> <20200610100756.GO494336@umbus.fritz.box> <858e9554-a4c7-6487-121b-ac3eaa209cb7@redhat.com> 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=2020-06-10_07:2020-06-10, 2020-06-10 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 suspectscore=0 cotscore=-2147483648 mlxlogscore=999 clxscore=1015 malwarescore=0 impostorscore=0 bulkscore=0 spamscore=0 lowpriorityscore=0 mlxscore=0 priorityscore=1501 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006100095 Received-SPF: pass client-ip=148.163.158.5; envelope-from=pasic@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/10 08:25:00 X-ACL-Warn: Detected OS = Linux 3.1-3.10 [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=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" , Claudio Imbrenda , Richard Henderson , Cornelia Huck , qemu-devel@nongnu.org, Christian Borntraeger , qemu-s390x@nongnu.org, Viktor Mihajlovski , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 10 Jun 2020 12:24:14 +0200 David Hildenbrand wrote: > On 10.06.20 12:07, David Gibson wrote: > > On Wed, Jun 10, 2020 at 09:22:45AM +0200, David Hildenbrand wrote: > >> On 10.06.20 06:31, David Gibson wrote: > >>> On Tue, Jun 09, 2020 at 12:44:39PM -0400, Michael S. Tsirkin wrote: > >>>> On Tue, Jun 09, 2020 at 06:28:39PM +0200, Halil Pasic wrote: > >>>>> 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). > >>>> > >>>> So if we want to keep it user friendly, there could be > >>>> protection property with values on/off/auto, and auto > >>>> would poke at host capability to figure out whether > >>>> it's supported. > >>>> > >>>> Both virtio and CPU would inherit from that. > >>> > >>> Right, that's what I have in mind for my 'host-trust-limitation' > >>> property (a generalized version of the existing 'memory-encryption' > >>> machine option). My draft patches already set virtio properties > >>> accordingly, it should be possible to set (default) cpu properties as > >>> well. > >> > >> No crazy CPU model hacks please (at least speaking for the s390x). > > > > Uh... I'm not really sure what you have in mind here. > > > > Reading along I got the impression that we want to glue the availability > of CPU features to other QEMU cmdline parameters (besides the > accelerator). ("to set (default) cpu properties as well"). If we are > talking about other CPU properties not expressed as CPU features (e.g., > -cpu X,Y=on ...), then there is no issue. > I share the concerns broght forward by David.