Re: [PATCH v4 2/4] vhost-vsock-pci: force virtio version 1

[Cornelia Huck]

On Mon, 21 Sep 2020 10:38:05 +0200
Stefano Garzarella <sgarzare@redhat.com> wrote:

> Commit 9b3a35ec82 ("virtio: verify that legacy support is not
> accidentally on") added a safety check that requires to set
> 'disable-legacy=on' on vhost-vsock-pci device:
> 
>     $ ./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
> 
> virtio-vsock was introduced after the release of VIRTIO 1.0
> specifications, so it should be 'modern-only'.
> In addition Cornelia verified that forcing a legacy mode on
> vhost-vsock-pci device using x86-64 host and s390x guest, so with
> different endianness, produces strange behaviours.
> 
> This patch forces virtio version 1 and removes the 'transitional_name'
> property removing the need to specify 'disable-legacy=on' on
> vhost-vsock-pci device.
> 
> To avoid migration issues, we force virtio version 1 only when
> legacy check is enabled in the new machine types (>= 5.1).

Maybe add

"As the transitional device name is not commonly used, we do not
provide compatibility handling for it." ?

> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Qian Cai <caiqian@redhat.com>
> Reported-by: Qinghua Cheng <qcheng@redhat.com>
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1868449
> Suggested-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> v3:
>  - forced virtio version 1 only with new machine types
> v2:
>  - fixed commit message [Cornelia]
> ---
>  hw/virtio/vhost-vsock-pci.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 

Reviewed-by: Cornelia Huck <cohuck@redhat.com>