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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 3 Mar 2020 12:42:51 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06avi18626390.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 023Cfq6C50856286 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 3 Mar 2020 12:41:52 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4F4B511C04C; Tue, 3 Mar 2020 12:42:50 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 158FC11C050; Tue, 3 Mar 2020 12:42:50 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.219]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 3 Mar 2020 12:42:50 +0000 (GMT) Subject: Re: [PATCH v5 07/18] s390x: protvirt: Inhibit balloon when switching to protected mode To: Cornelia Huck , Janosch Frank References: <20200226122038.61481-1-frankja@linux.ibm.com> <20200226122038.61481-8-frankja@linux.ibm.com> <9e8c83c2-5d17-2887-4073-698c12c40e79@de.ibm.com> <53287b24-6cab-2110-226c-f10cef3c8eb0@redhat.com> <556c23cb-7648-f4f6-aef4-728a164d9502@linux.ibm.com> <20200226192404.57b6ef61.cohuck@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200226192404.57b6ef61.cohuck@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 20030312-0008-0000-0000-00000358E814 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20030312-0009-0000-0000-00004A7A16F1 Message-Id: <1f8e0553-5593-15bb-3a79-1b2bb8557aa9@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-03-03_04:2020-03-03, 2020-03-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 clxscore=1015 priorityscore=1501 mlxlogscore=999 malwarescore=0 impostorscore=0 suspectscore=0 lowpriorityscore=0 bulkscore=0 spamscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003030096 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 148.163.158.5 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: Halil Pasic , qemu-s390x@nongnu.org, qemu-devel@nongnu.org, David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 26.02.20 19:24, Cornelia Huck wrote: > On Wed, 26 Feb 2020 16:30:32 +0100 > Janosch Frank wrote: > >> On 2/26/20 4:16 PM, David Hildenbrand wrote: >>> On 26.02.20 16:06, Christian Borntraeger wrote: >>>> >>>> >>>> On 26.02.20 15:59, David Hildenbrand wrote: >>>>> On 26.02.20 13:20, Janosch Frank wrote: >>>>>> Ballooning in protected VMs can only be done when the guest shares the >>>>>> pages it gives to the host. Hence, until we have a solution for this >>>>>> in the guest kernel, we inhibit ballooning when switching into >>>>>> protected mode and reverse that once we move out of it. >>>>> >>>>> I don't understand what you mean here, sorry. zapping a page will mean >>>>> that a fresh one will be faulted in when accessed. And AFAIK, that means >>>>> it will be encrypted again when needed. >>>>> >>>>> Is that more like the UV will detect this as an integrity issue and >>>>> crash the VM? >>>> >>>> yes, the UV will detect a fresh page as an integrity issue. >>>> Only if the page was defined to be shared by the guest, we would avoid the >>>> integrity check. >>>> >>> >>> Please make that clearer in the patch description. With that >>> >>> Reviewed-by: David Hildenbrand >>> >> >> How about: >> s390x: protvirt: Inhibit balloon when switching to protected mode >> >> Ballooning in protected VMs can only be done when the guest shares the >> pages it gives to the host. If pages are not shared, the integrity >> checks will fail once those pages have been altered and are given back >> to the guest. > > This makes sense to me... > >> >> Hence, until we have a solution for this in the guest kernel, we >> inhibit ballooning when switching into protected mode and reverse that >> once we move out of it. > > ...however, I'm scratching my head here. > > If we have a future guest that knows how to handle this, how do we > know? We know that the current Linux driver clears > VIRTIO_F_IOMMU_PLATFORM during feature negotiation, and presumably a > guest that knows how to handle this will not do that. But it still > won't work as expected, as we inhibit ballooning... > > So, either > - we don't inhibit ballooning now; any guest that clears the (required) > virtio feature bit won't be able to drive the virtio-balloon device > anyway, but a future guest that negotiates the bit would work; or > - we inhibit ballooning now; no guest can therefore use ballooning, > regardless what they are doing or not doing (this includes guests > that negotiate the feature bit, but fail to handle pages properly). > > Or is there some other reason why we need to inhibit ballooning for > protected vms? So here is my proposal. 1. we block ballooning now in QEMU (take this patch now) 2. Later Halil will provide a change to virtio that removes the blocker and adds VIRTIO_F_IOMMU_PLATFORM automatically by QEMU when doing the protvirt switch. This is ok as the guest balloon driver will reject to work with the IOMMU change (see https://lore.kernel.org/qemu-devel/20200227132402.67a38047.pasic@linux.ibm.com/) 3. later we can fix the guest balloon driver to do the right thing for this case (e.g. do the make shared call)