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Tsirkin" , gautam.dawar@amd.com, Jason Wang , Laurent Vivier Subject: Re: [PATCH] virtio-net: clear guest_announce feature if no cvq backend In-Reply-To: <20230124161159.2182117-1-eperezma@redhat.com> ("Eugenio =?utf-8?Q?P=C3=A9rez=22's?= message of "Tue, 24 Jan 2023 17:11:59 +0100") References: <20230124161159.2182117-1-eperezma@redhat.com> Date: Wed, 25 Jan 2023 14:38:22 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: AM4PR0101CA0076.eurprd01.prod.exchangelabs.com (2603:10a6:200:41::44) To DS7PR10MB4926.namprd10.prod.outlook.com (2603:10b6:5:3ac::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR10MB4926:EE_|BY5PR10MB4275:EE_ X-MS-Office365-Filtering-Correlation-Id: 4760c169-d963-4fbc-21cb-08dafee1d20d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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X-Proofpoint-GUID: 6ClDWOAH-FHnwmChTKW6IzNVXg6-2QyK X-Proofpoint-ORIG-GUID: 6ClDWOAH-FHnwmChTKW6IzNVXg6-2QyK Received-SPF: pass client-ip=205.220.165.32; envelope-from=david.edmondson@oracle.com; helo=mx0a-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-Mailman-Approved-At: Wed, 25 Jan 2023 10:15:50 -0500 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tuesday, 2023-01-24 at 17:11:59 +01, Eugenio P=C3=A9rez wrote: > Since GUEST_ANNOUNCE is emulated the feature bit could be set without > backend support. This happens in the vDPA case. > > However, backend vDPA parent may not have CVQ support. This causes an > incoherent feature set, and the driver may refuse to start. This > happens in virtio-net Linux driver. Could you now simplify the tests in virtio_net_announce() and virtio_net_post_load_device() to look only for the presence of GUEST_ANNOUNCE, given that you can now presume that it implies CTRL_VQ? But anyway: Reviewed-by: David Edmondson > This may be solved differently in the future. Qemu is able to emulate a > CVQ just for guest_announce purposes, helping guest to notify the new > location with vDPA devices that does not support it. However, this is > left as a TODO as it is way more complex to backport. > > Tested with vdpa_net_sim, toggling manually VIRTIO_NET_F_CTRL_VQ in the > driver and migrating it with x-svq=3Don. > > Fixes: 980003debddd ("vdpa: do not handle VIRTIO_NET_F_GUEST_ANNOUNCE in = vhost-vdpa") > Reported-by: Dawar, Gautam > Signed-off-by: Eugenio P=C3=A9rez > --- > hw/net/virtio-net.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > index 3ae909041a..09d5c7a664 100644 > --- a/hw/net/virtio-net.c > +++ b/hw/net/virtio-net.c > @@ -820,6 +820,21 @@ static uint64_t virtio_net_get_features(VirtIODevice= *vdev, uint64_t features, > features |=3D (1ULL << VIRTIO_NET_F_MTU); > } > > + /* > + * Since GUEST_ANNOUNCE is emulated the feature bit could be set wit= hout > + * enabled. This happens in the vDPA case. > + * > + * Make sure the feature set is not incoherent, as the driver could = refuse > + * to start. > + * > + * TODO: QEMU is able to emulate a CVQ just for guest_announce purpo= ses, > + * helping guest to notify the new location with vDPA devices that d= oes not > + * support it. > + */ > + if (!virtio_has_feature(vdev->backend_features, VIRTIO_NET_F_CTRL_VQ= )) { > + virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE); > + } > + > return features; > } --=20 Why stay in college? Why go to night school?