Re: [PATCH net-next v8] virtio_net: Support RX hash XDP hint

[Jason Wang]

On Tue, Apr 16, 2024 at 2:20 PM Liang Chen <liangchen.linux@xxxxxxxxx> wrote:
>
> The RSS hash report is a feature that's part of the virtio specification.
> Currently, virtio backends like qemu, vdpa (mlx5), and potentially vhost
> (still a work in progress as per [1]) support this feature. While the
> capability to obtain the RSS hash has been enabled in the normal path,
> it's currently missing in the XDP path. Therefore, we are introducing
> XDP hints through kfuncs to allow XDP programs to access the RSS hash.
>
> 1.
> https://lore.kernel.org/all/20231015141644.260646-1-akihiko.odaki@xxxxxxxxxx/#r
>
> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> ---
>   Changes from v7:
> - use table lookup for rss hash type
>   Changes from v6:
> - fix a coding style issue
>   Changes from v5:
> - Preservation of the hash value has been dropped, following the conclusion
>   from discussions in V3 reviews. The virtio_net driver doesn't
>   accessing/using the virtio_net_hdr after the XDP program execution, so
>   nothing tragic should happen. As to the xdp program, if it smashes the
>   entry in virtio header, it is likely buggy anyways. Additionally, looking
>   up the Intel IGC driver,  it also does not bother with this particular
>   aspect.
> ---
>  drivers/net/virtio_net.c        | 42 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_net.h |  1 +
>  2 files changed, 43 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c22d1118a133..1d750009f615 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4621,6 +4621,47 @@ static void virtnet_set_big_packets(struct virtnet_info *vi, const int mtu)
>         }
>  }
>
> +static enum xdp_rss_hash_type
> +virtnet_xdp_rss_type[VIRTIO_NET_HASH_REPORT_MAX_TABLE] = {
> +       [VIRTIO_NET_HASH_REPORT_NONE] = XDP_RSS_TYPE_NONE,
> +       [VIRTIO_NET_HASH_REPORT_IPv4] = XDP_RSS_TYPE_L3_IPV4,
> +       [VIRTIO_NET_HASH_REPORT_TCPv4] = XDP_RSS_TYPE_L4_IPV4_TCP,
> +       [VIRTIO_NET_HASH_REPORT_UDPv4] = XDP_RSS_TYPE_L4_IPV4_UDP,
> +       [VIRTIO_NET_HASH_REPORT_IPv6] = XDP_RSS_TYPE_L3_IPV6,
> +       [VIRTIO_NET_HASH_REPORT_TCPv6] = XDP_RSS_TYPE_L4_IPV6_TCP,
> +       [VIRTIO_NET_HASH_REPORT_UDPv6] = XDP_RSS_TYPE_L4_IPV6_UDP,
> +       [VIRTIO_NET_HASH_REPORT_IPv6_EX] = XDP_RSS_TYPE_L3_IPV6_EX,
> +       [VIRTIO_NET_HASH_REPORT_TCPv6_EX] = XDP_RSS_TYPE_L4_IPV6_TCP_EX,
> +       [VIRTIO_NET_HASH_REPORT_UDPv6_EX] = XDP_RSS_TYPE_L4_IPV6_UDP_EX
> +};
> +
> +static int virtnet_xdp_rx_hash(const struct xdp_md *_ctx, u32 *hash,
> +                              enum xdp_rss_hash_type *rss_type)
> +{
> +       const struct xdp_buff *xdp = (void *)_ctx;
> +       struct virtio_net_hdr_v1_hash *hdr_hash;
> +       struct virtnet_info *vi;
> +       u16 hash_report;
> +
> +       if (!(xdp->rxq->dev->features & NETIF_F_RXHASH))
> +               return -ENODATA;
> +
> +       vi = netdev_priv(xdp->rxq->dev);
> +       hdr_hash = (struct virtio_net_hdr_v1_hash *)(xdp->data - vi->hdr_len);
> +       hash_report = __le16_to_cpu(hdr_hash->hash_report);
> +
> +       if (hash_report >= VIRTIO_NET_HASH_REPORT_MAX_TABLE)
> +               hash_report = VIRTIO_NET_HASH_REPORT_NONE;
> +
> +       *rss_type = virtnet_xdp_rss_type[hash_report];
> +       *hash = __le32_to_cpu(hdr_hash->hash_value);
> +       return 0;
> +}
> +
> +static const struct xdp_metadata_ops virtnet_xdp_metadata_ops = {
> +       .xmo_rx_hash                    = virtnet_xdp_rx_hash,
> +};
> +
>  static int virtnet_probe(struct virtio_device *vdev)
>  {
>         int i, err = -ENOMEM;
> @@ -4747,6 +4788,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>                                   VIRTIO_NET_RSS_HASH_TYPE_UDP_EX);
>
>                 dev->hw_features |= NETIF_F_RXHASH;
> +               dev->xdp_metadata_ops = &virtnet_xdp_metadata_ops;
>         }
>
>         if (vi->has_rss_hash_report)
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index cc65ef0f3c3e..3ee695450096 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -176,6 +176,7 @@ struct virtio_net_hdr_v1_hash {
>  #define VIRTIO_NET_HASH_REPORT_IPv6_EX         7
>  #define VIRTIO_NET_HASH_REPORT_TCPv6_EX        8
>  #define VIRTIO_NET_HASH_REPORT_UDPv6_EX        9
> +#define VIRTIO_NET_HASH_REPORT_MAX_TABLE      10

This should not be part of uAPI. It may confuse the userspace.

Others look good.

Thanks

>         __le16 hash_report;
>         __le16 padding;
>  };
> --
> 2.40.1
>