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Wed, 28 Apr 2021 19:24:35 +0000 From: Raphael Norwitz To: Kevin Wolf Subject: Re: [PATCH 4/5] virtio: Fail if iommu_platform is requested, but unsupported Thread-Topic: [PATCH 4/5] virtio: Fail if iommu_platform is requested, but unsupported Thread-Index: AQHXN5lWW/llp3lkL06gnwadtyn+KqrKWQeA Date: Wed, 28 Apr 2021 19:24:32 +0000 Message-ID: <20210428192431.GC20605@raphael-debian-dev> References: <20210422170221.285006-1-kwolf@redhat.com> <20210422170221.285006-5-kwolf@redhat.com> In-Reply-To: <20210422170221.285006-5-kwolf@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mutt/1.10.1 (2018-07-13) authentication-results: redhat.com; dkim=none (message not signed) header.d=none;redhat.com; dmarc=none action=none header.from=nutanix.com; x-originating-ip: [69.122.45.60] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 547014a8-4ca4-4eea-6f05-08d90a7b420e x-ms-traffictypediagnostic: SN1PR02MB3821: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-proofpoint-crosstenant: true x-ms-oob-tlc-oobclassifiers: OLM:9508; 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envelope-from=raphael.norwitz@nutanix.com; helo=mx0a-002c1b01.pphosted.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.22, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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: "den-plotnikov@yandex-team.ru" , "mst@redhat.com" , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" , Raphael Norwitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 22, 2021 at 07:02:20PM +0200, Kevin Wolf wrote: > Commit 2943b53f6 (' virtio: force VIRTIO_F_IOMMU_PLATFORM') made sure > that vhost can't just reject VIRTIO_F_IOMMU_PLATFORM when it was > requested. However, just adding it back to the negotiated flags isn't > right either because it promises support to the guest that the device > actually doesn't support. One example of a vhost-user device that > doesn't have support for the flag is the vhost-user-blk export of QEMU. >=20 > Instead of successfully creating a device that doesn't work, just fail > to plug the device when it doesn't support the feature, but it was > requested. This results in much clearer error messages. >=20 > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=3D1935031 > Signed-off-by: Kevin Wolf > --- > hw/virtio/virtio-bus.c | 5 +++++ > 1 file changed, 5 insertions(+) >=20 > diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c > index d6332d45c3..859978d248 100644 > --- a/hw/virtio/virtio-bus.c > +++ b/hw/virtio/virtio-bus.c > @@ -69,6 +69,11 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Err= or **errp) > return; > } > Can you explain this check a little more? Above we have: bool has_iommu =3D virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM); and then we get the host features from the bckend: vdev->host_features =3D vdc->get_features(vdev, vdev->host_features So as is this is catching the case where vdev->host_features had VIRTIO_F_IOMMU_PLATFORM set before (by default?), but doesn't now that the features have been retrieved?=20 Why not just: if (!virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) { > + if (has_iommu && !virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATF= ORM)) { > + error_setg(errp, "iommu_platform=3Dtrue is not supported by the = device"); > + return; > + } > + > if (klass->device_plugged !=3D NULL) { > klass->device_plugged(qbus->parent, &local_err); > } > --=20 > 2.30.2 > =