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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 3 Mar 2020 14:44:21 -0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 023EiK5a59113716 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 3 Mar 2020 14:44:20 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 15854A404D; Tue, 3 Mar 2020 14:44:20 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CD606A4040; Tue, 3 Mar 2020 14:44:19 +0000 (GMT) Received: from oc2783563651 (unknown [9.152.224.80]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 3 Mar 2020 14:44:19 +0000 (GMT) Date: Tue, 3 Mar 2020 15:44:18 +0100 From: Halil Pasic To: "Michael S. Tsirkin" Subject: Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM In-Reply-To: <20200227104233-mutt-send-email-mst@kernel.org> References: <20200226094357.25061-1-jasowang@redhat.com> <20200226142839.4263de9b.pasic@linux.ibm.com> <20200226083654-mutt-send-email-mst@kernel.org> <20200226163618.31aa86ed.pasic@linux.ibm.com> <20200226115009-mutt-send-email-mst@kernel.org> <20200227140215.2d12149c.pasic@linux.ibm.com> <20200227104233-mutt-send-email-mst@kernel.org> 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-cbid: 20030314-0016-0000-0000-000002ECCDDA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20030314-0017-0000-0000-000033501584 Message-Id: <20200303154418.43317b1d.pasic@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-03-03_05:2020-03-03, 2020-03-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxlogscore=999 lowpriorityscore=0 suspectscore=0 phishscore=0 mlxscore=0 impostorscore=0 bulkscore=0 malwarescore=0 adultscore=0 clxscore=1015 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003030110 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 148.163.156.1 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: Tom Lendacky , Jason Wang , qemu-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 27 Feb 2020 10:47:22 -0500 "Michael S. Tsirkin" wrote: > On Thu, Feb 27, 2020 at 02:02:15PM +0100, Halil Pasic wrote: > > On Wed, 26 Feb 2020 11:52:26 -0500 > > "Michael S. Tsirkin" wrote: > > > > > On Wed, Feb 26, 2020 at 04:36:18PM +0100, Halil Pasic wrote: > > > > On Wed, 26 Feb 2020 08:37:13 -0500 > > > > "Michael S. Tsirkin" wrote: > > > > > > > > > On Wed, Feb 26, 2020 at 02:28:39PM +0100, Halil Pasic wrote: > > > > > > On Wed, 26 Feb 2020 17:43:57 +0800 > > > > > > Jason Wang wrote: > > > > > > > > > > > > > We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on > > > > > > > platform without IOMMU support. This can lead unnecessary IOTLB > > > > > > > transactions which will damage the performance. > > > > > > > > > > > > > > Fixing this by check whether the device is backed by IOMMU and disable > > > > > > > device IOTLB. > > > > > > > > > > > > > > Reported-by: Halil Pasic > > > > > > > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support") > > > > > > > Cc: qemu-stable@nongnu.org > > > > > > > Signed-off-by: Jason Wang > > > > > > > > > > > > Tested-by: Halil Pasic > > > > > > Reviewed-by: Halil Pasic > > > > > > > > > > > > Thank you very much for fixing this! BTW as I mentioned before it > > > > > > fixes vhost-vsock with iommu_platform=on as well. > > > > > > > > > > Fixes as in improves performance? > > > > > > > > No, fixes like one does not get something like: > > > > qemu-system-s390x: vhost_set_features failed: Operation not supported (95) > > > > qemu-system-s390x: Error starting vhost: 95 > > > > any more. > > > > > > > > Regards, > > > > Halil > > > > > > > > [..] > > > > > > But can commit c471ad0e9bd46 actually boot a secure guest > > > where iommu_platform=on is required? > > > > > > > No, of course it can not. But I'm not sure about AMD SEV. AFAIU without > > Jason's patch it does not work for AMD SEV. Tom already stated that with > > SEV they don't need the IOVA translation aspect of ACCESS_PLATFORM, but > > I have no idea if the condition vdev->dma_as == &address_space_memory > > catches them as well or not. They probably have !=. > > > > CCing Tom. @Tom does vhost-vsock work for you with SEV and current qemu? > > > > Also, one can specify iommu_platform=on on a device that ain't a part of > > a secure-capable VM, just for the fun of it. And that breaks > > vhost-vsock. Or is setting iommu_platform=on only valid if > > qemu-system-s390x is protected virtualization capable? > > > > BTW, I don't have a strong opinion on the fixes tag. We currently do not > > recommend setting iommu_platform, and thus I don't think we care too > > much about past qemus having problems with it. > > > > Regards, > > Halil > > > Let's just say if we do have a Fixes: tag we want to set it correctly to > the commit that needs this fix. > You are absolutely correct. And c471ad0e9bd46 has nothing to do with vsock. On s390x the situation with virtio-net + vhost + iommu_platform=on seems rather complex. I did some digging, but I have no conclusive results yet. And I don't think we care all that much for iommu_platform=on for old qemus. Regards, Halil