Re: [PATCH v1] virtio-net: Fix to avoid using reserved feature bits

On 1/26/25 7:20 AM, Parav Pandit wrote:
> @@ -136,6 +124,18 @@ \subsection{Feature bits}\label{sec:Device Types / Network Device / Feature bits
>  \item[VIRTIO_NET_F_SPEED_DUPLEX(63)] Device reports speed and duplex.
>  
>  \item[VIRTIO_NET_F_RSS_CONTEXT(64)] Device supports multiple RSS contexts.
> +
> +\item[VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO (65)] Driver can receive GSO packets
> +  carried by a UDP tunnel.
> +
> +\item[VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM (66)] Driver handles packets
> +  carried by a UDP tunnel with partial csum for the outer header.
> +
> +\item[VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO (67)] Device can receive GSO packets
> +  carried by a UDP tunnel.
> +
> +\item[VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM (68)] Device handles packets
> +  carried by a UDP tunnel with partial csum for the outer header.
>  \end{description}

I'm finally trying to finalize the implementation and I must admit I
underlooked the implication of using features bit >= 64.

AFAICS all the virtio drivers in the Linux kernel and qemu assume that
the features can be represented with a single u64.

Supporting the above requires major reworks in both user-space and
kernel space. At least on the kernel side a similar rework (extending
the _netdev_ features field) has proven to be complex enough to defeat
any implementation attempts for years and in the end it was dismissed in
favor of lower bits reuse.

I'm wondering if we could reconsider using reserved bits here?

Thanks!

Paolo