On Thu, Jul 28, 2022 at 11:09:15AM +0200, Claudio Fontana wrote: > On 7/28/22 09:43, 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? > > > > 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, > > while QEMU is left hanging waiting forever for a response to > > VHOST_USER_GET_VRING_BASE issued as a result of vhost_net_stop. > > > > Just saying, I am having more success with the second ordering, but I am > > still studying, don't have the full picture yet. > > > Currently I'm doing (on top of Michael's patch) the following which seems to > be working > (but of course this does not even being to look at the other transports, > architectures etc), > just an idea to share: > > --- > hw/virtio/virtio-pci.c | 7 ++++--- > hw/virtio/virtio.c | 7 ++++++- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 3189ec014d..3cbfa3ce3a 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -312,6 +312,7 @@ static void virtio_ioport_write(void *opaque, uint32_t > addr, uint32_t val) > case VIRTIO_PCI_QUEUE_PFN: > pa = (hwaddr)val << VIRTIO_PCI_QUEUE_ADDR_SHIFT; > if (pa == 0) { > + virtio_bus_reset(&proxy->bus); > virtio_pci_reset(DEVICE(proxy)); > } > else > @@ -1941,11 +1942,8 @@ static void virtio_pci_exit(PCIDevice *pci_dev) > 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); > msix_unuse_all_vectors(&proxy->pci_dev); > > for (i = 0; i < VIRTIO_QUEUE_MAX; i++) { > @@ -1960,7 +1958,10 @@ static void virtio_pci_reset(DeviceState *qdev) > static void virtio_pci_bus_reset(DeviceState *qdev) > { > PCIDevice *dev = PCI_DEVICE(qdev); > + VirtIOPCIProxy *proxy = VIRTIO_PCI(qdev); > + VirtioBusState *bus = VIRTIO_BUS(&proxy->bus); > > + virtio_bus_reset(bus); > virtio_pci_reset(qdev); > > if (pci_is_express(dev)) { > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 5d607aeaa0..da58ca6f86 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -1977,6 +1977,12 @@ int virtio_set_status(VirtIODevice *vdev, uint8_t val) > VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev); > trace_virtio_set_status(vdev, val); > > + if (val == 0) { > + VirtioBusState *bus = VIRTIO_BUS(qdev_get_parent_bus(DEVICE(vdev))); > + virtio_bus_reset(bus); > + return 0; > + } > + > if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { > if (!(vdev->status & VIRTIO_CONFIG_S_FEATURES_OK) && > val & VIRTIO_CONFIG_S_FEATURES_OK) { > @@ -2025,7 +2031,6 @@ void virtio_reset(void *opaque) > VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev); > int i; > > - virtio_set_status(vdev, 0); > if (current_cpu) { > /* Guest initiated reset */ > vdev->device_endian = virtio_current_cpu_endian(); > -- > 2.26.2
As you say this is incomplete ... bout could you share a bit more of what issue does this address? -- MST
