On Thu, 13 Aug 2020 11:16:56 +0200
Stefano Garzarella <sgarz...@redhat.com> wrote:
> Hi,
>
> Qinghua discovered that virtio-vsock-pci requires 'disable-legacy=on' in
> QEMU 5.1:
> $ ./qemu-system-x86_64 ... -device vhost-vsock-pci,guest-cid=5
> qemu-system-x86_64: -device vhost-vsock-pci,guest-cid=5:
> device is modern-only, use disable-legacy=on
>
> Bisecting I found that this behaviour starts from this commit:
> 9b3a35ec82 ("virtio: verify that legacy support is not accidentally on")
Oh, I had heard that from others already, was still trying to figure
out what to do.
>
> IIUC virtio-vsock is modern-only, so I tried this patch and it works:
>
> diff --git a/hw/virtio/vhost-user-vsock-pci.c
> b/hw/virtio/vhost-user-vsock-pci.c
> index f4cf95873d..6e4cc874cd 100644
> --- a/hw/virtio/vhost-user-vsock-pci.c
> +++ b/hw/virtio/vhost-user-vsock-pci.c
> @@ -40,6 +40,7 @@ static void vhost_user_vsock_pci_realize(VirtIOPCIProxy
> *vpci_dev, Error **errp)
> VHostUserVSockPCI *dev = VHOST_USER_VSOCK_PCI(vpci_dev);
> DeviceState *vdev = DEVICE(&dev->vdev);
>
> + virtio_pci_force_virtio_1(vpci_dev);
> qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
> }
>
> diff --git a/hw/virtio/vhost-vsock-pci.c b/hw/virtio/vhost-vsock-pci.c
> index a815278e69..f641b974e9 100644
> --- a/hw/virtio/vhost-vsock-pci.c
> +++ b/hw/virtio/vhost-vsock-pci.c
> @@ -44,6 +44,7 @@ static void vhost_vsock_pci_realize(VirtIOPCIProxy
> *vpci_dev, Error **errp)
> VHostVSockPCI *dev = VHOST_VSOCK_PCI(vpci_dev);
> DeviceState *vdev = DEVICE(&dev->vdev);
>
> + virtio_pci_force_virtio_1(vpci_dev);
> qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
> }
>
>
> Do you think this is the right approach or is there a better way to
> solve this issue?
We basically have three possible ways to deal with this:
- Force it to modern (i.e., what you have been doing; would need the
equivalent changes in ccw as well.)
Pro: looks like the cleanest approach.
Con: not sure if we would need backwards compatibility support,
which looks hairy.
- Add vsock to the list of devices with legacy support.
Pro: Existing setups continue to work.
Con: If vsock is really virtio-1-only, we still carry around
possibly broken legacy support.
- Do nothing, have users force legacy off. Bad idea, as ccw has no way
to do that on the command line.
The first option is probably best.
