[PATCH v4] virtio_net: Support RX hash XDP hint

[Liang Chen]

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>
Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/net/virtio_net.c | 98 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 86 insertions(+), 12 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d7ce4a1011ea..7ce666c86ee0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -349,6 +349,12 @@ struct virtio_net_common_hdr {
 	};
 };
 
+struct virtnet_xdp_buff {
+	struct xdp_buff xdp;
+	__le32 hash_value;
+	__le16 hash_report;
+};
+
 static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
 
 static bool is_xdp_frame(void *ptr)
@@ -1033,6 +1039,16 @@ static void put_xdp_frags(struct xdp_buff *xdp)
 	}
 }
 
+static void virtnet_xdp_save_rx_hash(struct virtnet_xdp_buff *virtnet_xdp,
+				     struct net_device *dev,
+				     struct virtio_net_hdr_v1_hash *hdr_hash)
+{
+	if (dev->features & NETIF_F_RXHASH) {
+		virtnet_xdp->hash_value = hdr_hash->hash_value;
+		virtnet_xdp->hash_report = hdr_hash->hash_report;
+	}
+}
+
 static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
 			       struct net_device *dev,
 			       unsigned int *xdp_xmit,
@@ -1199,9 +1215,10 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 	unsigned int headroom = vi->hdr_len + header_offset;
 	struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
 	struct page *page = virt_to_head_page(buf);
+	struct virtnet_xdp_buff virtnet_xdp;
 	struct page *xdp_page;
+	struct xdp_buff *xdp;
 	unsigned int buflen;
-	struct xdp_buff xdp;
 	struct sk_buff *skb;
 	unsigned int metasize = 0;
 	u32 act;
@@ -1233,17 +1250,20 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 		page = xdp_page;
 	}
 
-	xdp_init_buff(&xdp, buflen, &rq->xdp_rxq);
-	xdp_prepare_buff(&xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
+	xdp = &virtnet_xdp.xdp;
+	xdp_init_buff(xdp, buflen, &rq->xdp_rxq);
+	xdp_prepare_buff(xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
 			 xdp_headroom, len, true);
 
-	act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
+	virtnet_xdp_save_rx_hash(&virtnet_xdp, dev, (void *)hdr);
+
+	act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
 
 	switch (act) {
 	case XDP_PASS:
 		/* Recalculate length in case bpf program changed it */
-		len = xdp.data_end - xdp.data;
-		metasize = xdp.data - xdp.data_meta;
+		len = xdp->data_end - xdp->data;
+		metasize = xdp->data - xdp->data_meta;
 		break;
 
 	case XDP_TX:
@@ -1254,7 +1274,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
 		goto err_xdp;
 	}
 
-	skb = virtnet_build_skb(buf, buflen, xdp.data - buf, len);
+	skb = virtnet_build_skb(buf, buflen, xdp->data - buf, len);
 	if (unlikely(!skb))
 		goto err;
 
@@ -1591,10 +1611,11 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 	int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
 	struct page *page = virt_to_head_page(buf);
 	int offset = buf - page_address(page);
+	struct virtnet_xdp_buff virtnet_xdp;
 	unsigned int xdp_frags_truesz = 0;
 	struct sk_buff *head_skb;
 	unsigned int frame_sz;
-	struct xdp_buff xdp;
+	struct xdp_buff *xdp;
 	void *data;
 	u32 act;
 	int err;
@@ -1604,16 +1625,19 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 	if (unlikely(!data))
 		goto err_xdp;
 
-	err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
+	xdp = &virtnet_xdp.xdp;
+	err = virtnet_build_xdp_buff_mrg(dev, vi, rq, xdp, data, len, frame_sz,
 					 &num_buf, &xdp_frags_truesz, stats);
 	if (unlikely(err))
 		goto err_xdp;
 
-	act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
+	virtnet_xdp_save_rx_hash(&virtnet_xdp, dev, (void *)hdr);
+
+	act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
 
 	switch (act) {
 	case XDP_PASS:
-		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
+		head_skb = build_skb_from_xdp_buff(dev, vi, xdp, xdp_frags_truesz);
 		if (unlikely(!head_skb))
 			break;
 		return head_skb;
@@ -1626,7 +1650,7 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
 		break;
 	}
 
-	put_xdp_frags(&xdp);
+	put_xdp_frags(xdp);
 
 err_xdp:
 	put_page(page);
@@ -4579,6 +4603,55 @@ 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 virtnet_xdp_buff *virtnet_xdp = (void *)_ctx;
+
+	if (!(virtnet_xdp->xdp.rxq->dev->features & NETIF_F_RXHASH))
+		return -ENODATA;
+
+	switch (__le16_to_cpu(virtnet_xdp->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(virtnet_xdp->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;
@@ -4704,6 +4777,7 @@ 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)
-- 
2.42.0