[PATCH RFC 3/8] vsock/virtio: implement the datagram data path

[Sergio Lopez <slp@redhat.com>]

Add the datagram feature bit and packet type, and implement the common
virtio transport operations needed to bind, send, and receive
datagrams.

Send each message as an OP_RW packet with a maximum 64 KiB payload,
including support for empty messages. Bound pending sends by the
socket send buffer instead of connection-oriented peer credits. Charge
pending payload bytes before handing the skb to the backend and
release that charge exactly once on completion, rejection, or queued
drops.

Deliver incoming datagrams through the bound table without entering
the connection state machine. Validate the transport and connected
peer under the socket lock, including after shutdown, and silently
discard undeliverable messages. Use the socket datagram queue for
recvmsg(), including source addresses, peeking, and truncation
reporting based on the payload length after socket filtering.  Reject
MSG_OOB and MSG_ERRQUEUE before accessing the receive queue.  Reject
datagram sockmap admission until its receive callbacks support it.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 include/linux/virtio_vsock.h            |   2 +
 include/uapi/linux/virtio_vsock.h       |   2 +
 net/vmw_vsock/virtio_transport_common.c | 150 +++++++++++++++++++++++++++++---
 net/vmw_vsock/vsock_bpf.c               |   3 +-
 4 files changed, 142 insertions(+), 15 deletions(-)

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index f91704731057..0bccae661221 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -12,6 +12,8 @@
 struct virtio_vsock_skb_cb {
 	bool reply;
 	bool tap_delivered;
+	/* Datagram payload is still charged to bytes_unsent. */
+	bool tx_accounted;
 	u32 offset;
 };
 
diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
index 64738838bee5..27b4b2b8bf13 100644
--- a/include/uapi/linux/virtio_vsock.h
+++ b/include/uapi/linux/virtio_vsock.h
@@ -40,6 +40,7 @@
 
 /* The feature bitmap for virtio vsock */
 #define VIRTIO_VSOCK_F_SEQPACKET	1	/* SOCK_SEQPACKET supported */
+#define VIRTIO_VSOCK_F_DGRAM		3	/* SOCK_DGRAM supported */
 
 struct virtio_vsock_config {
 	__le64 guest_cid;
@@ -69,6 +70,7 @@ struct virtio_vsock_hdr {
 enum virtio_vsock_type {
 	VIRTIO_VSOCK_TYPE_STREAM = 1,
 	VIRTIO_VSOCK_TYPE_SEQPACKET = 2,
+	VIRTIO_VSOCK_TYPE_DGRAM = 3,
 };
 
 enum virtio_vsock_op {
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 1e762a480df4..ae33630d99e7 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -204,10 +204,18 @@ static u16 virtio_transport_get_type(struct sock *sk)
 {
 	if (sk->sk_type == SOCK_STREAM)
 		return VIRTIO_VSOCK_TYPE_STREAM;
+	else if (sk->sk_type == SOCK_DGRAM)
+		return VIRTIO_VSOCK_TYPE_DGRAM;
 	else
 		return VIRTIO_VSOCK_TYPE_SEQPACKET;
 }
 
+static void virtio_transport_dgram_skb_destructor(struct sk_buff *skb)
+{
+	virtio_transport_consume_skb_sent(skb, false);
+	sock_wfree(skb);
+}
+
 /* Returns new sk_buff on success, otherwise returns NULL. */
 static struct sk_buff *virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
 						  size_t payload_len,
@@ -303,6 +311,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	u32 src_cid, src_port, dst_cid, dst_port;
 	const struct virtio_transport *t_ops;
 	struct iov_iter_state msg_iter_state;
+	struct sock *sk = sk_vsock(vsk);
 	struct virtio_vsock_sock *vvs;
 	struct ubuf_info *uarg = NULL;
 	u32 pkt_len = info->pkt_len;
@@ -329,12 +338,24 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 
 	vvs = vsk->trans;
 
-	/* virtio_transport_get_credit might return less than pkt_len credit */
-	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
+	if (info->type == VIRTIO_VSOCK_TYPE_DGRAM) {
+		if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
+			return -EMSGSIZE;
 
-	/* Do not send zero length OP_RW pkt */
-	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
-		return pkt_len;
+		/* Datagram sends are serialized by the socket lock. */
+		if (sk_wmem_alloc_get(sk) >= READ_ONCE(sk->sk_sndbuf)) {
+			sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
+			set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+			return -EAGAIN;
+		}
+	} else {
+		/* virtio_transport_get_credit might return less than pkt_len credit */
+		pkt_len = virtio_transport_get_credit(vvs, pkt_len);
+
+		/* Do not send zero length OP_RW pkt */
+		if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
+			return pkt_len;
+	}
 
 	if (info->msg && (info->msg->msg_flags & MSG_ZEROCOPY)) {
 		/* If 'info->msg' is not NULL, this is only VIRTIO_VSOCK_OP_RW.
@@ -348,7 +369,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 			uarg = msg_zerocopy_realloc(sk_vsock(vsk), pkt_len,
 						    NULL, false);
 			if (!uarg) {
-				virtio_transport_put_credit(vvs, pkt_len);
+				if (info->type != VIRTIO_VSOCK_TYPE_DGRAM)
+					virtio_transport_put_credit(vvs, pkt_len);
 				return -ENOMEM;
 			}
 
@@ -393,7 +415,15 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 			break;
 		}
 
-		virtio_transport_inc_tx_pkt(vvs, skb);
+		if (info->type == VIRTIO_VSOCK_TYPE_DGRAM) {
+			spin_lock_bh(&vvs->tx_lock);
+			vvs->bytes_unsent += skb_len;
+			spin_unlock_bh(&vvs->tx_lock);
+			VIRTIO_VSOCK_SKB_CB(skb)->tx_accounted = true;
+			skb->destructor = virtio_transport_dgram_skb_destructor;
+		} else {
+			virtio_transport_inc_tx_pkt(vvs, skb);
+		}
 
 		ret = t_ops->send_pkt(skb, info->net);
 		if (ret < 0)
@@ -416,7 +446,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (info->msg && ret < 0)
 		iov_iter_restore(&info->msg->msg_iter, &msg_iter_state);
 
-	virtio_transport_put_credit(vvs, rest_len);
+	if (info->type != VIRTIO_VSOCK_TYPE_DGRAM)
+		virtio_transport_put_credit(vvs, rest_len);
 
 	/* msg_zerocopy_realloc() initializes the ubuf_info refcnt to 1.
 	 * skb_zcopy_set() increases it for each skb, so we can drop that
@@ -620,7 +651,9 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
 {
 	struct sock *s = skb->sk;
 
-	if (s && skb->len) {
+	if (s && skb->len &&
+	    (s->sk_type != SOCK_DGRAM ||
+	     VIRTIO_VSOCK_SKB_CB(skb)->tx_accounted)) {
 		struct vsock_sock *vs = vsock_sk(s);
 		struct virtio_vsock_sock *vvs;
 
@@ -631,6 +664,9 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume)
 		spin_unlock_bh(&vvs->tx_lock);
 	}
 
+	if (s && s->sk_type == SOCK_DGRAM)
+		VIRTIO_VSOCK_SKB_CB(skb)->tx_accounted = false;
+
 	if (consume)
 		consume_skb(skb);
 }
@@ -999,7 +1035,47 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
 			       struct msghdr *msg,
 			       size_t len, int flags)
 {
-	return -EOPNOTSUPP;
+	struct sock *sk = sk_vsock(vsk);
+	struct virtio_vsock_hdr *hdr;
+	struct sk_buff *skb;
+	size_t payload_len;
+	int err;
+
+	if (flags & (MSG_OOB | MSG_ERRQUEUE))
+		return -EOPNOTSUPP;
+
+	skb = skb_recv_datagram(sk, flags, &err);
+	if (!skb)
+		return err;
+
+	hdr = virtio_vsock_hdr(skb);
+	payload_len = skb->len;
+
+	if (payload_len > len) {
+		payload_len = len;
+		msg->msg_flags |= MSG_TRUNC;
+	}
+
+	err = skb_copy_datagram_iter(skb, 0, &msg->msg_iter, payload_len);
+	if (err)
+		goto out;
+
+	if (msg->msg_name) {
+		DECLARE_SOCKADDR(struct sockaddr_vm *, vm_addr, msg->msg_name);
+
+		vsock_addr_init(vm_addr, le64_to_cpu(hdr->src_cid),
+				le32_to_cpu(hdr->src_port));
+		msg->msg_namelen = sizeof(*vm_addr);
+	}
+
+	if (flags & MSG_TRUNC)
+		err = skb->len;
+	else
+		err = payload_len;
+
+out:
+	skb_free_datagram(sk, skb);
+	return err;
 }
 EXPORT_SYMBOL_GPL(virtio_transport_dgram_dequeue);
 
@@ -1202,13 +1278,13 @@ EXPORT_SYMBOL_GPL(virtio_transport_stream_is_active);
 int virtio_transport_dgram_bind(struct vsock_sock *vsk,
 				struct sockaddr_vm *addr)
 {
-	return -EOPNOTSUPP;
+	return vsock_bind_common(vsk, addr);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
 
 bool virtio_transport_dgram_allow(struct vsock_sock *vsk, u32 cid, u32 port)
 {
-	return false;
+	return true;
 }
 EXPORT_SYMBOL_GPL(virtio_transport_dgram_allow);
 
@@ -1246,7 +1322,17 @@ virtio_transport_dgram_enqueue(struct vsock_sock *vsk,
 			       struct msghdr *msg,
 			       size_t dgram_len)
 {
-	return -EOPNOTSUPP;
+	struct virtio_vsock_pkt_info info = {
+		.op = VIRTIO_VSOCK_OP_RW,
+		.msg = msg,
+		.pkt_len = dgram_len,
+		.vsk = vsk,
+		.remote_cid = remote_addr->svm_cid,
+		.remote_port = remote_addr->svm_port,
+		.net = sock_net(sk_vsock(vsk)),
+	};
+
+	return virtio_transport_send_pkt_info(vsk, &info);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_dgram_enqueue);
 
@@ -1771,7 +1857,8 @@ virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb,
 static bool virtio_transport_valid_type(u16 type)
 {
 	return (type == VIRTIO_VSOCK_TYPE_STREAM) ||
-	       (type == VIRTIO_VSOCK_TYPE_SEQPACKET);
+	       (type == VIRTIO_VSOCK_TYPE_SEQPACKET) ||
+	       (type == VIRTIO_VSOCK_TYPE_DGRAM);
 }
 
 /* We are under the virtio-vsock's vsock->rx_lock or vhost-vsock's vq->mutex
@@ -1805,6 +1892,41 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
 		goto free_pkt;
 	}
 
+	/* Dgram packets are delivered directly to bound sockets without
+	 * going through the connection state machine. Undeliverable
+	 * datagrams are silently dropped (no RST).
+	 */
+	if (le16_to_cpu(hdr->type) == VIRTIO_VSOCK_TYPE_DGRAM) {
+		if (le16_to_cpu(hdr->op) != VIRTIO_VSOCK_OP_RW)
+			goto free_pkt;
+
+		sk = vsock_find_bound_socket_net(&dst, net);
+
+		if (!sk || sk->sk_type != SOCK_DGRAM) {
+			if (sk)
+				sock_put(sk);
+			goto free_pkt;
+		}
+
+		vsk = vsock_sk(sk);
+		lock_sock(sk);
+		if (sock_flag(sk, SOCK_DEAD) ||
+		    vsk->transport != &t->transport ||
+		    (sk->sk_socket->state != SS_UNCONNECTED &&
+		     !vsock_check_source(vsk, &t->transport, &src))) {
+			release_sock(sk);
+			sock_put(sk);
+			goto free_pkt;
+		}
+
+		if (sock_queue_rcv_skb(sk, skb))
+			kfree_skb(skb);
+
+		release_sock(sk);
+		sock_put(sk);
+		return;
+	}
+
 	/* The socket must be in connected or bound table
 	 * otherwise send reset back
 	 */
diff --git a/net/vmw_vsock/vsock_bpf.c b/net/vmw_vsock/vsock_bpf.c
index 9049d2648646..296e1fa7970b 100644
--- a/net/vmw_vsock/vsock_bpf.c
+++ b/net/vmw_vsock/vsock_bpf.c
@@ -161,7 +161,8 @@ int vsock_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore
 	if (!vsk->transport)
 		return -ENODEV;
 
-	if (!vsk->transport->read_skb)
+	/* Datagram receive is not implemented by the sockmap callbacks. */
+	if (sk->sk_type == SOCK_DGRAM || !vsk->transport->read_skb)
 		return -EOPNOTSUPP;
 
 	vsock_bpf_check_needs_rebuild(psock->sk_proto);

-- 
2.56.0