Re: [PATCH] vdpa: dont check vhost_vdpa->suspended when unsupported

[Eugenio Perez Martin]

On Wed, Jun 7, 2023 at 11:09 AM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>
> When read the state of a virtqueue, vhost_vdpa need
> to check whether the device is suspended.
>
> This commit verifies whether VHOST_BACKEND_F_SUSPEND is
> negotiated when checking vhost_vdpa->suspended.
>

I'll add: Otherwise, qemu prints XXX error message.

On second thought, not returning an error prevents the caller
(vhost.c:vhost_virtqueue_stop) from recovering used idx from the
guest.

I'm not sure about the right fix for this, should we call
virtio_queue_restore_last_avail_idx here? Communicate that the backend
cannot suspend so vhost.c can print a better error message?

Thanks!

> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  hw/virtio/vhost-vdpa.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index b3094e8a8b..ae176c06dd 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1397,7 +1397,7 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev 
> *dev,
>          return 0;
>      }
>
> -    if (!v->suspended) {
> +    if ((dev->backend_cap & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) && 
> (!v->suspended)) {
>          /*
>           * Cannot trust in value returned by device, let vhost recover used
>           * idx from guest.
> --
> 2.39.1
>