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

[Liang Chen <liangchen.linux@gmail.com>]

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;
+	}
+
+	*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)
-- 
2.40.1