Re: [RFC PATCH v5 21/26] vhost: Add vhost_svq_valid_guest_features to shadow vq

[Jason Wang]

On Sat, Oct 30, 2021 at 2:44 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> This allows it to test if the guest has aknowledge an invalid transport
> feature for SVQ. This will include packed vq layout or event_idx,
> where VirtIO device needs help from SVQ.
>
> There is not needed at this moment, but since SVQ will not re-negotiate
> features again with the guest, a failure in acknowledge them is fatal
> for SVQ.
>

It's not clear to me why we need this. Maybe you can give me an
example. E.g isn't it sufficient to filter out the device with
event_idx?

Thanks

> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-shadow-virtqueue.h | 1 +
>  hw/virtio/vhost-shadow-virtqueue.c | 6 ++++++
>  2 files changed, 7 insertions(+)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> b/hw/virtio/vhost-shadow-virtqueue.h
> index 946b2c6295..ac55588009 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -16,6 +16,7 @@
>  typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
>
>  bool vhost_svq_valid_device_features(uint64_t *features);
> +bool vhost_svq_valid_guest_features(uint64_t *features);
>
>  void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
>  void vhost_svq_set_guest_call_notifier(VhostShadowVirtqueue *svq, int 
> call_fd);
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index 6e0508a231..cb9ffcb015 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -62,6 +62,12 @@ bool vhost_svq_valid_device_features(uint64_t 
> *dev_features)
>      return true;
>  }
>
> +/* If the guest is using some of these, SVQ cannot communicate */
> +bool vhost_svq_valid_guest_features(uint64_t *guest_features)
> +{
> +    return true;
> +}
> +
>  /* Forward guest notifications */
>  static void vhost_handle_guest_kick(EventNotifier *n)
>  {
> --
> 2.27.0
>