Re: [PATCH] virtio_net: Support RX hash XDP hint

[Heng Qi]

Hi Liang Chen,

在 2024/1/22 下午6:22, Liang Chen 写道:
> 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.
>
> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> ---
>   drivers/net/virtio_net.c | 56 ++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 56 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index d7ce4a1011ea..1463a4709e3c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4579,6 +4579,60 @@ 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))

I think 'vi->has_rss_hash_report' should be used here.
NETIF_F_RXHASH cannot guarantee that the hash report feature is negotiated,
and accessing hash_report and hash_value is unsafe at this time.

> +		return -ENODATA;
> +
> +	vi = netdev_priv(xdp->rxq->dev);
> +	hdr_hash = (struct virtio_net_hdr_v1_hash *)(xdp->data - vi->hdr_len);

If the virtio-net-hdr is overrided by the XDP prog, how can this be done 
correctly and as expected?

Thanks,
Heng

> +
> +	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;
> +	}
> +
> +	*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;
> @@ -4613,6 +4667,8 @@ static int virtnet_probe(struct virtio_device *vdev)
>   	dev->ethtool_ops = &virtnet_ethtool_ops;
>   	SET_NETDEV_DEV(dev, &vdev->dev);
>   
> +	dev->xdp_metadata_ops = &virtnet_xdp_metadata_ops;
> +
>   	/* Do we support "hardware" checksums? */
>   	if (virtio_has_feature(vdev, VIRTIO_NET_F_CSUM)) {
>   		/* This opens up the world of extra features. */