[PATCH] vhost/net: Fill virtio_net_hdr GSO/csum metadata on RX

[weimin xiong <15927021679@163.com>]

From: xiongweimin <xiongweimin@kylinos.cn>

When VHOST_NET_F_VIRTIO_NET_HDR is set, vhost supplies virtio_net_hdr to
the guest but previously always wrote a zeroed header (GSO_NONE). Guests
that rely on GUEST_TSO*/GUEST_CSUM therefore never saw offload metadata.

Peek the socket skb before recvmsg and populate the header with
virtio_net_hdr_from_skb(). Also advertise the corresponding guest offload
feature bits from VHOST_GET_FEATURES.

TX TSO toward backends without IFF_VNET_HDR is intentionally left for a
follow-up series.

Signed-off-by: xiongweimin <xiongweimin@kylinos.cn>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: virtualization@vger.kernel.org
Cc: netdev@vger.kernel.org
---

--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -73,6 +73,10 @@
 	VHOST_FEATURES,
 	VHOST_NET_F_VIRTIO_NET_HDR,
 	VIRTIO_NET_F_MRG_RXBUF,
+	VIRTIO_NET_F_GUEST_CSUM,
+	VIRTIO_NET_F_GUEST_TSO4,
+	VIRTIO_NET_F_GUEST_TSO6,
+	VIRTIO_NET_F_GUEST_ECN,
 	VIRTIO_F_ACCESS_PLATFORM,
 	VIRTIO_F_RING_RESET,
 	VIRTIO_F_IN_ORDER,
@@ -644,7 +648,7 @@
 static size_t init_iov_iter(struct vhost_virtqueue *vq, struct iov_iter *iter,
 			    size_t hdr_size, int out)
 {
-	/* Skip header. TODO: support TSO. */
+	/* Skip guest virtio_net_hdr; TX TSO handled in a follow-up. */
 	size_t len = iov_length(vq->iov, out);
 
 	iov_iter_init(iter, ITER_SOURCE, vq->iov, out, len);
@@ -1025,6 +1029,35 @@
 	return len;
 }
 
+/*
+ * When VHOST_NET_F_VIRTIO_NET_HDR is set, vhost supplies virtio_net_hdr.
+ * Populate GSO/checksum metadata from the socket skb so guests that
+ * negotiated GUEST_TSO*/GUEST_CSUM receive correct offload information.
+ */
+static int vhost_net_hdr_from_sock(struct vhost_virtqueue *vq, struct sock *sk,
+				   struct virtio_net_hdr *hdr)
+{
+	struct sk_buff *skb;
+	unsigned long flags;
+	int vlan_hlen = 0;
+	int ret;
+
+	spin_lock_irqsave(&sk->sk_receive_queue.lock, flags);
+	skb = skb_peek(&sk->sk_receive_queue);
+	if (!skb) {
+		spin_unlock_irqrestore(&sk->sk_receive_queue.lock, flags);
+		memset(hdr, 0, sizeof(*hdr));
+		hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE;
+		return 0;
+	}
+	if (skb_vlan_tag_present(skb))
+		vlan_hlen = VLAN_HLEN;
+	ret = virtio_net_hdr_from_skb(skb, hdr, vhost_is_little_endian(vq),
+				      true, vlan_hlen);
+	spin_unlock_irqrestore(&sk->sk_receive_queue.lock, flags);
+	return ret;
+}
+
 static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
 				      bool *busyloop_intr, unsigned int *count)
 {
@@ -1239,10 +1272,18 @@
 		/* We don't need to be notified again. */
 		iov_iter_init(&msg.msg_iter, ITER_DEST, vq->iov, in, vhost_len);
 		fixup = msg.msg_iter;
-		if (unlikely((vhost_hlen))) {
-			/* We will supply the header ourselves
-			 * TODO: support TSO.
+		if (unlikely(vhost_hlen)) {
+			/*
+			 * Build virtio_net_hdr from the socket skb before
+			 * recvmsg consumes it. Skip for ptr_ring backends
+			 * where the skb is not on sk_receive_queue.
 			 */
+			if (!nvq->rx_ring &&
+			    vhost_net_hdr_from_sock(vq, sock->sk, &hdr)) {
+				vq_err(vq, "Failed to build vnet_hdr from skb\n");
+				vhost_discard_vq_desc(vq, headcount, ndesc);
+				continue;
+			}
 			iov_iter_advance(&msg.msg_iter, vhost_hlen);
 		}
 		err = sock->ops->recvmsg(sock, &msg,
@@ -1270,7 +1311,6 @@
 			 */
 			iov_iter_advance(&fixup, sizeof(hdr));
 		}
-		/* TODO: Should check and handle checksum. */
 
 		num_buffers = cpu_to_vhost16(vq, headcount);
 		if (likely(set_num_buffers) &&