On Tue, Jan 24, 2023 at 5:32 PM Eugenio Pérez <epere...@redhat.com> wrote:
>
> Since GUEST_ANNOUNCE is emulated the feature bit could be set without
> backend support. This happens in the vDPA case.
>
> However, backend vDPA parent may not have CVQ support. This causes an
> incoherent feature set, and the driver may refuse to start. This
> happens in virtio-net Linux driver.
>
> This may be solved differently in the future. Qemu is able to emulate a
> CVQ just for guest_announce purposes, helping guest to notify the new
> location with vDPA devices that does not support it. However, this is
> left as a TODO as it is way more complex to backport.
>
> Tested with vdpa_net_sim, toggling manually VIRTIO_NET_F_CTRL_VQ in the
> driver and migrating it with x-svq=on.
>
Friendly ping about this patch, as it fell through the cracks if I'm not wrong.
Thanks!
> Fixes: 980003debddd ("vdpa: do not handle VIRTIO_NET_F_GUEST_ANNOUNCE in
> vhost-vdpa")
> Reported-by: Dawar, Gautam <gautam.da...@amd.com>
> Signed-off-by: Eugenio Pérez <epere...@redhat.com>
> ---
> hw/net/virtio-net.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 3ae909041a..09d5c7a664 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -820,6 +820,21 @@ static uint64_t virtio_net_get_features(VirtIODevice
> *vdev, uint64_t features,
> features |= (1ULL << VIRTIO_NET_F_MTU);
> }
>
> + /*
> + * Since GUEST_ANNOUNCE is emulated the feature bit could be set without
> + * enabled. This happens in the vDPA case.
> + *
> + * Make sure the feature set is not incoherent, as the driver could
> refuse
> + * to start.
> + *
> + * TODO: QEMU is able to emulate a CVQ just for guest_announce purposes,
> + * helping guest to notify the new location with vDPA devices that does
> not
> + * support it.
> + */
> + if (!virtio_has_feature(vdev->backend_features, VIRTIO_NET_F_CTRL_VQ)) {
> + virtio_clear_feature(&features, VIRTIO_NET_F_GUEST_ANNOUNCE);
> + }
> +
> return features;
> }
>
> --
> 2.31.1
>
>
