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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20200528132112.2a1fdf45.cohuck@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="yzFN00To9H82ZFoiYdugMhih1XYJ4IdHQ" X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216, 18.0.687 definitions=2020-05-28_03:2020-05-28, 2020-05-28 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 clxscore=1015 mlxlogscore=999 spamscore=0 priorityscore=1501 cotscore=-2147483648 malwarescore=0 mlxscore=0 lowpriorityscore=0 phishscore=0 suspectscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005280097 Received-SPF: pass client-ip=148.163.158.5; envelope-from=frankja@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/28 10:42:58 X-ACL-Warn: Detected OS = Linux 3.x [generic] 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, 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 , Pierre Morel , David Hildenbrand , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Christian Borntraeger , qemu-s390x@nongnu.org, Viktor Mihajlovski , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --yzFN00To9H82ZFoiYdugMhih1XYJ4IdHQ Content-Type: multipart/mixed; boundary="cWSGx8k2xeUTRpi64GMfvO0LLj2hdg8lg" --cWSGx8k2xeUTRpi64GMfvO0LLj2hdg8lg Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 5/28/20 1:21 PM, Cornelia Huck wrote: > On Fri, 22 May 2020 23:04:51 +0200 > Halil Pasic wrote: >=20 >> On Wed, 20 May 2020 12:23:24 -0400 >> "Michael S. Tsirkin" wrote: >> >>> On Fri, May 15, 2020 at 12:11:55AM +0200, Halil Pasic wrote: =20 >>>> The virtio specification tells that the device is to present >>>> VIRTIO_F_ACCESS_PLATFORM (a.k.a. VIRTIO_F_IOMMU_PLATFORM) when the >>>> device "can only access certain memory addresses with said access >>>> specified and/or granted by the platform". This is the case for a >>>> protected VMs, as the device can access only memory addresses that a= re >>>> in pages that are currently shared (only the guest can share/unsare = its >>>> pages). >>>> >>>> No VM, however, starts out as a protected VM, but some VMs may be >>>> converted to protected VMs if the guest decides so. >>>> >>>> Making the end user explicitly manage the VIRTIO_F_ACCESS_PLATFORM v= ia >>>> the property iommu_on is a minor disaster. Since the correctness of = the >>>> paravirtualized virtio devices depends (and thus in a sense the >>>> correctness of the hypervisor) it, then the hypervisor should have t= he >>>> last word about whether VIRTIO_F_ACCESS_PLATFORM is to be presented = or >>>> not. =20 >>> >>> So, how about this: switch iommu to on/off/auto. =20 >> >> Many thanks for the reveiw, and sorry about the delay on my side. We >> have holidays here in Germany and I was not motivated enough up until >> now to check on my mails. >> >> >> I've actually played with the thought of switching iommu_platform to = >> 'on/off/auto', but I didn't find an easy way to do it. I will look >> again. This would be the first property of this kind in QEMU, or? >=20 > virtio-pci uses it for 'disable-legacy'. >=20 >> >> The 'on/off/auto' would be certainly much cleaner form user-interface >> perspective. The downsides are that it is more invasive, and more >> complicated. I'm afraid that it would also leave more possibilities fo= r >> user error. >=20 > To me, on/off/auto sounds like a reasonable thing to do. >=20 > What possibilities of 'user error' do you see? Shouldn't we fence off > misconfigurations, if the consequences would be disastrous? >=20 >> >>> Add a property with a >>> reasonable name "allow protected"? If set allow switch to protected >>> memory and also set iommu auto to on by default. If not set then don= 't. >>> =20 >> >> I think we have "allow protected" already expressed via cpu models. I'= m >> also not sure how libvirt would react to the idea of a new machine >> property for this. You did mean "allow protected" as machine property,= >> or? >=20 > "Unpack facility in cpu model" means "guest may transition into pv > mode", right? What does it look like when the guest actually has > transitioned? Well, we don't sync the features that the protected guest has back into QEMU. So basically the VM doesn't really change except for ms->pv now being true. >=20 >> >> AFAIU "allow protected" would be required for the !PV to PV switch, an= d >> we would have to reject paravirtualized devices with iommu_platform=3D= 'off' >> on VM construction or hotplug (iommu_platform=3D'auto/on' would be fin= e). >> >> Could you please confirm that I understood this correctly? >> >> >>> This will come handy for other things like migrating to hosts without= >>> protected memory support. >>> =20 >> >> This is already covered by cpu model AFAIK. >=20 > I don't think we'd want to migrate between pv and non-pv anyway? What exactly do you mean by that? I'd expect that the VM can either be migrated in PV or non-PV mode and not in a transition phase. >=20 >> >>> >>> Also, virtio now calls this PLATFORM_ACCESS, maybe we should rename >>> the property (keeping old one around for compat)? =20 >> >> You mean the like rename 'iommu_platform' to 'platform_access'? I like= >> the idea, but I'm not sure libvirt will like it as well. Boris any >> opinions? >> >>> I feel this will address lots of complaints ... >>> =20 >>>> Currently presenting a PV guest with a (paravirtualized) virtio-ccw >>>> device has catastrophic consequences for the VM (after the hyperviso= rs >>>> access to protected memory). This is especially grave in case of dev= ice >>>> hotplug (because in this case the guest is more likely to be in the >>>> middle of something important). >>>> >>>> Let us manage the VIRTIO_F_ACCESS_PLATFORM virtio feature automatica= lly >>>> for virtio-ccw devices, i.e. force it before we start the protected = VM. >>>> If the VM should cease to be protected, the original value is restor= ed. >>>> >>>> Signed-off-by: Halil Pasic =20 >>> >>> >>> I don't really understand things fully but it looks like you are >>> changing features of a device. If so this bothers me, resets >>> happen at random times while driver is active, and we never >>> expect features to change. >>> =20 >> >> Changing the device features is IMHO all right because the features ca= n >> change only immediately after a system reset and before the first vCPU= >> is run. That is ensured by two facts. >> >> >> First, the feature can only change when ms->pv changes. That is on the= >> first reset after the VM entered or left the "protected virtualization= " >> mode of operation. And that switch requires a system reset. Because th= e >> PV switch is initiated by the guest, and the guest is rebooted as a >> consequence, the guest will never observe the change in features. >=20 > This really needs more comments, as it is not obvious to the casual > reader. (I also stumbled over the resets.) >=20 > But I wonder whether we are actually missing those subsystems resets > today? >=20 >=20 --cWSGx8k2xeUTRpi64GMfvO0LLj2hdg8lg-- --yzFN00To9H82ZFoiYdugMhih1XYJ4IdHQ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEwGNS88vfc9+v45Yq41TmuOI4ufgFAl7PzeoACgkQ41TmuOI4 ufiy8xAAjZTPBYb6PPIKbfUeoUKQObDZrb6VAFSBE2yCaCd0nymcMMYoaQw/ffHf ve5m6qrc15hJFWwneG60h7XKAU6kEAjFkHe5Og5+AFPY8rQUqs729YE0nuxa0GJi 6Ib7Fjw3y84gYZndOGr8kKksFvUUTLHVrzZJaaYenHCL4pH4HWB5gYyqCIgqX8Uq gXZNiuIO2C532c7F7l7yfzn5yKQocMIvCfnbFuj4WDsZDtKwOfCkTzOPld69/3VB fArjL9p2ALNtxOkn0e6bpanWzHMI1ev1ITMTVvfH4KJcMyWP+tcuk4eXkTnCg0FA Idy30OKWKe/8fCmu0V0VccoyzHA6L8ZGvO02/uu7aWUwXhrT/rv/PBbuy9gLEjhK fw1T8XsUwel743HXCsH+F0E6flPV5L1jMEjKN4OR/ArKOfTOScXOPtT4GUkbcPTc FWEF00AyHM5yb6e6/94BsvkENxNr1eZVsLTGXOlP2fx5VMnh4HLS17AfJlHVBI2J 5lcAD0oMUglYjOuim82IBwDS01+BMFHtsJMveKVbKIpv4R4fHUy+54ufQb7edCSD g6B9hy8Q9tjRCtz3N7hDRl8LMkVkljFNZ3JxkXMOzIBsEUef1ERAYaga6eFCF198 IonN75z9QSPQKApkVV4WUb1wDhi1XqSRVA6SNnnTqdyKv0aZJI4= =RhNU -----END PGP SIGNATURE----- --yzFN00To9H82ZFoiYdugMhih1XYJ4IdHQ--