On Thu, Jul 28, 2022 at 09:43:56AM +0200, Claudio Fontana wrote: > On 7/28/22 03:27, Jason Wang wrote: > > On Wed, Jul 27, 2022 at 11:32 PM Michael S. Tsirkin <m...@redhat.com> wrote: > >> > >> On Wed, Jul 27, 2022 at 12:51:31PM +0200, Claudio Fontana wrote: > >>> Hi Michael and all, > >>> > >>> I have started researching a qemu / ovs / dpdk bug: > >>> > >>> https://inbox.dpdk.org/dev/322122fb-619d-96f6-5c3e-9eabdbf38...@redhat.com/T/ > >>> > >>> that seems to be affecting multiple parties in the telco space, > >>> > >>> and during this process I noticed that qemu/hw/virtio/virtio.c does not > >>> do a full virtio reset > >>> in virtio_set_status, when receiving a status value of 0. > >>> > >>> It seems it has always been this way, so I am clearly missing / > >>> forgetting something basic, > >>> > >>> I checked the virtio spec at https://docs.oasis-open.org/ > >>> > >>> and from: > >>> > >>> " > >>> 4.1.4.3 Common configuration structure layout > >>> > >>> device_status > >>> The driver writes the device status here (see 2.1). Writing 0 into this > >>> field resets the device. > >>> > >>> " > >>> > >>> and > >>> > >>> " > >>> 2.4.1 Device Requirements: Device Reset > >>> A device MUST reinitialize device status to 0 after receiving a reset. > >>> " > >>> > >>> I would conclude that in virtio.c::virtio_set_status we should > >>> unconditionally do a full virtio_reset. > >>> > >>> Instead, we have just the check: > >>> > >>> if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) != > >>> (val & VIRTIO_CONFIG_S_DRIVER_OK)) { > >>> virtio_set_started(vdev, val & VIRTIO_CONFIG_S_DRIVER_OK); > >>> } > >>> > >>> which just sets the started field, > >>> > >>> and then we have the call to the virtio device class set_status > >>> (virtio_net...), > >>> but the VirtioDevice is not fully reset, as per the virtio_reset() call > >>> we are missing: > >>> > >>> " > >>> vdev->start_on_kick = false; > >>> vdev->started = false; > >>> vdev->broken = false; > >>> vdev->guest_features = 0; > >>> vdev->queue_sel = 0; > >>> vdev->status = 0; > >>> vdev->disabled = false; > >>> qatomic_set(&vdev->isr, 0); > >>> vdev->config_vector = VIRTIO_NO_VECTOR; > >>> virtio_notify_vector(vdev, vdev->config_vector); > >>> > >>> for(i = 0; i < VIRTIO_QUEUE_MAX; i++) { > >>> ... initialize vdev->vq[i] ... > >>> } > >>> " > >>> > >>> Doing a full reset seems to fix the problem for me, so I can send > >>> tentative patches if necessary, > >>> but what am I missing here? > >>> > >>> Thanks, > >>> > >>> Claudio > >>> > >>> -- > >>> Claudio Fontana > >>> Engineering Manager Virtualization, SUSE Labs Core > >>> > >>> SUSE Software Solutions Italy Srl > >> > >> > >> So for example for pci: > >> > >> case VIRTIO_PCI_STATUS: > >> > >> > >> .... > >> > >> if (vdev->status == 0) { > >> virtio_pci_reset(DEVICE(proxy)); > >> } > >> > >> which I suspect is a bug because: > >> > >> static void virtio_pci_reset(DeviceState *qdev) > >> { > >> VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev); > >> VirtioBusState *bus = VIRTIO_BUS(&proxy->bus); > >> PCIDevice *dev = PCI_DEVICE(qdev); > >> int i; > >> > >> virtio_bus_reset(bus); > > > > Note that we do virtio_reset() here. > > > Yes, thank you, I completely overlooked it, I noticed this in Michael's > response as well. > > However we end up with multiple calls to k->set_status, one from the > virtio_set_status call, > and one from the virtio_bus_reset(), which is probably something we don't > want. > > All in all it is not clear what the meaning of virtio_set_status is supposed > to be I think, > and I wonder what the assumptions are among all the callers. > If it is supposed to be an implementation of the virtio standard field as > described, I think we should do the reset right then and there, > but maybe the true meaning of the function is another one I couldn't > understand, since _some_ of the cases are processes there. > > And there is a question about ordering: > > in virtio_pci we end up calling virtio_set_status(0), which gets us > k->set_status(vdev, 0), which lands in virtio_net_set_status(0) and > virtio_net_vhost_status, > which causes a vhost_net_stop(). > Should we instead land in virtio_net_reset() first, by doing a virtio reset > earlier when detecting a 0 value from the driver?
Well we want to first stop the backend and only then reset our local state. Seems to make sense ... > in the scenario I am looking at (with vhost-user, ovs/dpdk, and a guest > testpmd application), > the guest application goes away without any chance to signal (kill -9), then > gets immediately restarted and does a write of 0 to status, while qemu and > ovs still hold the state for the device. > > As QEMU lands in vhost_net_stop(), it seems to cause a chain of events that > crash ovs which is trying to read an rx burst from the queue, Not sure I got this part. > while QEMU is left hanging waiting forever for a response to > VHOST_USER_GET_VRING_BASE issued as a result of vhost_net_stop. Ineteresting why doesn't socket close after ovs crash cause the read to fail. > Just saying, I am having more success with the second ordering, but I am > still studying, don't have the full picture yet. > > Thanks, > > Claudio > > > > >> msix_unuse_all_vectors(&proxy->pci_dev); > >> > >> for (i = 0; i < VIRTIO_QUEUE_MAX; i++) { > >> proxy->vqs[i].enabled = 0; > >> proxy->vqs[i].num = 0; > >> proxy->vqs[i].desc[0] = proxy->vqs[i].desc[1] = 0; > >> proxy->vqs[i].avail[0] = proxy->vqs[i].avail[1] = 0; > >> proxy->vqs[i].used[0] = proxy->vqs[i].used[1] = 0; > >> } > >> > >> > >> so far so good > >> > >> if (pci_is_express(dev)) { > >> pcie_cap_deverr_reset(dev); > >> pcie_cap_lnkctl_reset(dev); > >> > >> pci_set_word(dev->config + dev->exp.pm_cap + PCI_PM_CTRL, 0); > >> } > >> > >> this part is wrong I think, it got here by mistake since the same > >> function is used for bus level reset. > >> > >> Jason, Marcel, any input? > > > > Yes, I think we don't need PCI stuff here. We do virtio reset not pci. > > > > Thanks > > > >> > >> -- > >> MST > >> > > > >