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);
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?
--
MST
