On Sat, May 10, 2025 at 3:24 PM Akihiko Odaki <akihiko.od...@daynix.com> wrote:
>
> virtio_net_pre_load_queues() inspects vdev->guest_features to tell if
> VIRTIO_NET_F_RSS or VIRTIO_NET_F_MQ is enabled to infer the required
> number of queues. This works for VIRTIO_NET_F_MQ but it doesn't for
> VIRTIO_NET_F_RSS because only the lowest 32 bits of vdev->guest_features
> is set at the point and VIRTIO_NET_F_RSS uses bit 60 while
> VIRTIO_NET_F_MQ uses bit 22.
>
> Instead of inferring the required number of queues from
> vdev->guest_features, use the number loaded from the vm state.
>
> Fixes: 8c49756825da ("virtio-net: Add only one queue pair when realizing")
> Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>
> ---
> include/hw/virtio/virtio.h | 2 +-
> hw/net/virtio-net.c | 11 ++++-------
> hw/virtio/virtio.c | 14 +++++++-------
> 3 files changed, 12 insertions(+), 15 deletions(-)
>
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 638691028050..af52580c1e63 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -211,7 +211,7 @@ struct VirtioDeviceClass {
> int (*start_ioeventfd)(VirtIODevice *vdev);
> void (*stop_ioeventfd)(VirtIODevice *vdev);
> /* Called before loading queues. Useful to add queues before loading. */
> - int (*pre_load_queues)(VirtIODevice *vdev);
> + int (*pre_load_queues)(VirtIODevice *vdev, uint32_t n);
This turns out to be tricky as it has a lot of assumptions as
described in the changelog (e.g only lower 32bit of guest_features is
correct etc when calling this function).
Looking at the commit that introduces this which is 9379ea9db3c that says:
"""
Otherwise the loaded queues will not have handlers and elements
in them will not be processed.
"""
I fail to remember what it means or what happens if we don't do 9379ea9db3c.
Thanks
