Re: [PATCH net-next v7] virtio_net: Support RX hash XDP hint

Jesper Dangaard Brouer
2024-04-15T07:36:29Z

On 13/04/2024 06.10, Liang Chen 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@daynix.com/#r
>
> Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
> ---
> 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 | 55 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c22d1118a133..2a1892b7b8d3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4621,6 +4621,60 @@ static void virtnet_set_big_packets(struct virtnet_info *vi, const int mtu)
> }
> }
>
> +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;
> +
> + 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);
> +
> + switch (__le16_to_cpu(hdr_hash->hash_report)) {
> + case VIRTIO_NET_HASH_REPORT_TCPv4:
> + *rss_type = XDP_RSS_TYPE_L4_IPV4_TCP;
> + break;
> + case VIRTIO_NET_HASH_REPORT_UDPv4:
> + *rss_type = XDP_RSS_TYPE_L4_IPV4_UDP;
> + break;
> + case VIRTIO_NET_HASH_REPORT_TCPv6:
> + *rss_type = XDP_RSS_TYPE_L4_IPV6_TCP;
> + break;
> + case VIRTIO_NET_HASH_REPORT_UDPv6:
> + *rss_type = XDP_RSS_TYPE_L4_IPV6_UDP;
> + break;
> + case VIRTIO_NET_HASH_REPORT_TCPv6_EX:
> + *rss_type = XDP_RSS_TYPE_L4_IPV6_TCP_EX;
> + break;
> + case VIRTIO_NET_HASH_REPORT_UDPv6_EX:
> + *rss_type = XDP_RSS_TYPE_L4_IPV6_UDP_EX;
> + break;
> + case VIRTIO_NET_HASH_REPORT_IPv4:
> + *rss_type = XDP_RSS_TYPE_L3_IPV4;
> + break;
> + case VIRTIO_NET_HASH_REPORT_IPv6:
> + *rss_type = XDP_RSS_TYPE_L3_IPV6;
> + break;
> + case VIRTIO_NET_HASH_REPORT_IPv6_EX:
> + *rss_type = XDP_RSS_TYPE_L3_IPV6_EX;
> + break;
> + case VIRTIO_NET_HASH_REPORT_NONE:
> + default:
> + *rss_type = XDP_RSS_TYPE_NONE;
> + }

Why is this not implemented as a table lookup?

Like:

https://elixir.bootlin.com/linux/v6.9-rc4/source/drivers/net/ethernet/intel/igc/igc_main.c#L6652
https://elixir.bootlin.com/linux/latest/A/ident/xdp_rss_hash_type

--Jesper

> +
> + *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 +4801,7 @@ 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)