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Tsirkin" , Stefan Hajnoczi , Parav Pandit References: <20230112172434.760850-1-eperezma@redhat.com> <20230112172434.760850-7-eperezma@redhat.com> From: Jason Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, 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-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 在 2023/1/13 16:19, Eugenio Perez Martin 写道: > On Fri, Jan 13, 2023 at 5:36 AM Jason Wang wrote: >> On Fri, Jan 13, 2023 at 1:25 AM Eugenio Pérez wrote: >>> To restore the device at the destination of a live migration we send the >>> commands through control virtqueue. For a device to read CVQ it must >>> have received the DRIVER_OK status bit. >> This probably requires the support from the parent driver and requires >> some changes or fixes in the parent driver. >> >> Some drivers did: >> >> parent_set_status(): >> if (DRIVER_OK) >> if (queue_enable) >> write queue_enable to the device >> >> Examples are IFCVF or even vp_vdpa at least. MLX5 seems to be fine. >> > I don't get your point here. No device should start reading CVQ (or > any other VQ) without having received DRIVER_OK. If I understand the code correctly: For CVQ, we do SET_VRING_ENABLE before DRIVER_OK, that's fine. For datapath_vq, we do SET_VRING_ENABLE after DRIVER_OK, this requires parent driver support (explained above) > > Some parent drivers do not support sending the queue enable command > after DRIVER_OK, usually because they clean part of the state like the > set by set_vring_base. Even vdpa_net_sim needs fixes here. Yes, so the question is: Do we need another backend feature for this? (otherwise thing may break silently) > > But my understanding is that it should be supported so I consider it a > bug. Probably, we need fine some proof in the spec, e.g in 3.1.1: """ 7.Perform device-specific setup, including discovery of virtqueues for the device, optional per-bus setup, reading and possibly writing the device’s virtio configuration space, and population of virtqueues. 8.Set the DRIVER_OK status bit. At this point the device is “live”. """ So if my understanding is correct, "discovery of virtqueues for the device" implies queue_enable here which is expected to be done before DRIVER_OK. But it doesn't say anything regrading to the behaviour of setting queue ready after DRIVER_OK. I'm not sure it's a real bug or not, may Michael and comment on this. > Especially after queue_reset patches. Is that what you mean? We haven't supported queue_reset yet in Qemu. But it allows to write 1 to queue_enable after DRIVER_OK for sure. > >>> However this opens a window where the device could start receiving >>> packets in rx queue 0 before it receives the RSS configuration. To avoid >>> that, we will not send vring_enable until all configuration is used by >>> the device. >>> >>> As a first step, run vhost_set_vring_ready for all vhost_net backend after >>> all of them are started (with DRIVER_OK). This code should not affect >>> vdpa. >>> >>> Signed-off-by: Eugenio Pérez >>> --- >>> hw/net/vhost_net.c | 17 ++++++++++++----- >>> 1 file changed, 12 insertions(+), 5 deletions(-) >>> >>> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c >>> index c4eecc6f36..3900599465 100644 >>> --- a/hw/net/vhost_net.c >>> +++ b/hw/net/vhost_net.c >>> @@ -399,6 +399,18 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs, >>> } else { >>> peer = qemu_get_peer(ncs, n->max_queue_pairs); >>> } >>> + r = vhost_net_start_one(get_vhost_net(peer), dev); >>> + if (r < 0) { >>> + goto err_start; >>> + } >>> + } >>> + >>> + for (int j = 0; j < nvhosts; j++) { >>> + if (j < data_queue_pairs) { >>> + peer = qemu_get_peer(ncs, j); >>> + } else { >>> + peer = qemu_get_peer(ncs, n->max_queue_pairs); >>> + } >> I fail to understand why we need to change the vhost_net layer? This >> is vhost-vDPA specific, so I wonder if we can limit the changes to e.g >> vhost_vdpa_dev_start()? >> > The vhost-net layer explicitly calls vhost_set_vring_enable before > vhost_dev_start, and this is exactly the behavior we want to avoid. > Even if we make changes to vhost_dev, this change is still needed. Note that the only user of vhost_set_vring_enable() is vhost-user where the semantic is different: It uses that to changes the number of active queues: static int peer_attach(VirtIONet *n, int index)         if (nc->peer->info->type == NET_CLIENT_DRIVER_VHOST_USER) { =>      vhost_set_vring_enable(nc->peer, 1);     } This is not the semantic of vhost-vDPA that tries to be complaint with virtio-spec. So I'm not sure how it can help here. > > And we want to explicitly enable CVQ first, which "only" vhost_net > knows which is. This should be known by net/vhost-vdpa.c. > To perform that in vhost_vdpa_dev_start would require > quirks, involving one or more of: > * Ignore vq enable calls if the device is not the CVQ one. How to > signal what is the CVQ? Can we trust it will be the last one for all > kind of devices? > * Enable queues that do not belong to the last vhost_dev from the enable call. > * Enable the rest of the queues from the last enable in reverse order. > * Intercalate the "net load" callback between enabling the last > vhost_vdpa device and enabling the rest of devices. > * Add an "enable priority" order? Haven't had time in thinking through, but it would be better if we can limit the changes in vhost-vdpa layer. E.g currently the VHOST_VDPA_SET_VRING_ENABLE is done at vhost_dev_start(). Thanks > > Thanks! > >> Thanks >> >>> if (peer->vring_enable) { >>> /* restore vring enable state */ >>> @@ -408,11 +420,6 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs, >>> goto err_start; >>> } >>> } >>> - >>> - r = vhost_net_start_one(get_vhost_net(peer), dev); >>> - if (r < 0) { >>> - goto err_start; >>> - } >>> } >>> >>> return 0; >>> -- >>> 2.31.1 >>>