Date:   Wed, 19 Apr 2023 11:29:38 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Bobby Eshleman <bobby.eshleman@...edance.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Bryan Tan <bryantan@...are.com>,
        Vishnu Dasa <vdasa@...are.com>,
        VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH RFC net-next v2 1/4] virtio/vsock: support dgram

On Fri, Apr 14, 2023 at 12:25:57AM +0000, Bobby Eshleman wrote:
>This commit adds support for datagrams over virtio/vsock.
>
>Message boundaries are preserved on a per-skb and per-vq entry basis.
>Messages are copied in whole from the user to an SKB, which in turn is
>added to the scatterlist for the virtqueue in whole for the device.
>Messages do not straddle skbs and they do not straddle packets.
>Messages may be truncated by the receiving user if their buffer is
>shorter than the message.
>
>Other properties of vsock datagrams:
>- Datagrams self-throttle at the per-socket sk_sndbuf threshold.
>- The same virtqueue is used as is used for streams and seqpacket flows
>- Credits are not used for datagrams
>- Packets are dropped silently by the device, which means the virtqueue
>  will still get kicked even during high packet loss, so long as the
>  socket does not exceed sk_sndbuf.

So, IIUC the device will allocate the skb, then in
virtio_transport_recv_dgram(), when we call sock_queue_rcv_skb(),
if sk_rcvbuf is full, the skb is freed, right?

>
>Future work might include finding a way to reduce the virtqueue kick
>rate for datagram flows with high packet loss.
>
>One outstanding issue with this commit is that it re-uses the stream
>binding code and table, which means that there can not simultaneously be
>VSOCK dgram and VSOCK stream/seqpacket of same port and CID. This should
>be changed before undoing the RFC tag.

Okay, thanks for mentioning!

>
>Signed-off-by: Bobby Eshleman <bobby.eshleman@...edance.com>
>---
> drivers/vhost/vsock.c                   |   2 +-
> include/net/af_vsock.h                  |   1 +
> include/uapi/linux/virtio_vsock.h       |   1 +
> net/vmw_vsock/af_vsock.c                |  26 ++++-
> net/vmw_vsock/virtio_transport.c        |   2 +-
> net/vmw_vsock/virtio_transport_common.c | 199 ++++++++++++++++++++++++++++----
> 6 files changed, 204 insertions(+), 27 deletions(-)
>
>diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>index 6578db78f0ae..dff6ee1c479b 100644
>--- a/drivers/vhost/vsock.c
>+++ b/drivers/vhost/vsock.c
>@@ -921,7 +921,7 @@ static int __init vhost_vsock_init(void)
> 	int ret;
>
> 	ret = vsock_core_register(&vhost_transport.transport,
>-				  VSOCK_TRANSPORT_F_H2G);
>+				  VSOCK_TRANSPORT_F_H2G | VSOCK_TRANSPORT_F_DGRAM);

IIRC we don't support multiple VSOCK_TRANSPORT_F_DGRAM transports, so I
think we need to address also this case.

The problem with stream was that vmci_transport uses
MODULE_ALIAS_NETPROTO(PF_VSOCK). So, if a vsock socket is created before
any transports loaded, vmci_transport is automatically loaded, then we
can't laod any other transport providing F_DGRAM.

Maybe we can move vsock_core_register(..., VSOCK_TRANSPORT_F_DGRAM) in
vmci_vsock_transport_cb() for VMCI, but we need to think carefully
about it.

> 	if (ret < 0)
> 		return ret;
>
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index 0e7504a42925..57af28fede19 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -80,6 +80,7 @@ s64 vsock_stream_has_data(struct vsock_sock *vsk);
> s64 vsock_stream_has_space(struct vsock_sock *vsk);
> struct sock *vsock_create_connected(struct sock *parent);
> void vsock_data_ready(struct sock *sk);
>+int vsock_bind_stream(struct vsock_sock *vsk, struct sockaddr_vm *addr);
>
> /**** TRANSPORT ****/
>
>diff --git a/include/uapi/linux/virtio_vsock.h b/include/uapi/linux/virtio_vsock.h
>index 64738838bee5..331be28b1d30 100644
>--- a/include/uapi/linux/virtio_vsock.h
>+++ b/include/uapi/linux/virtio_vsock.h
>@@ -69,6 +69,7 @@ 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/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index 413407bb646c..46b3f35e3adc 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -677,6 +677,19 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
> 	return 0;
> }
>
>+int vsock_bind_stream(struct vsock_sock *vsk,
>+		      struct sockaddr_vm *addr)
>+{
>+	int retval;
>+
>+	spin_lock_bh(&vsock_table_lock);
>+	retval = __vsock_bind_connectible(vsk, addr);
>+	spin_unlock_bh(&vsock_table_lock);
>+
>+	return retval;
>+}
>+EXPORT_SYMBOL(vsock_bind_stream);
>+
> static int __vsock_bind_dgram(struct vsock_sock *vsk,
> 			      struct sockaddr_vm *addr)
> {
>@@ -2453,11 +2466,16 @@ int vsock_core_register(const struct vsock_transport *t, int features)
> 	}
>
> 	if (features & VSOCK_TRANSPORT_F_DGRAM) {
>-		if (t_dgram) {
>-			err = -EBUSY;
>-			goto err_busy;
>+		/* XXX: always chose the G2H variant over others, support nesting later */

Okay, please mention also in the commit description that we will fix
this before removing RFC.

>+		if (features & VSOCK_TRANSPORT_F_G2H) {
>+			if (t_dgram)
>+				pr_warn("vsock: preferring g2h transport for dgram\n");
>+			t_dgram = t;
>+		}
>+
>+		if (!t_dgram) {
>+			t_dgram = t;
> 		}
>-		t_dgram = t;
> 	}

Would be better to split this patch in 2 (changes in the core, changes
in virtio/vhost-vsock).

>
> 	if (features & VSOCK_TRANSPORT_F_LOCAL) {
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index e95df847176b..582c6c0f788f 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -775,7 +775,7 @@ static int __init virtio_vsock_init(void)
> 		return -ENOMEM;
>
> 	ret = vsock_core_register(&virtio_transport.transport,
>-				  VSOCK_TRANSPORT_F_G2H);
>+				  VSOCK_TRANSPORT_F_G2H | VSOCK_TRANSPORT_F_DGRAM);
> 	if (ret)
> 		goto out_wq;
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index e4878551f140..925acface893 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -37,6 +37,35 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
> 	return container_of(t, struct virtio_transport, transport);
> }
>
>+/* Requires info->msg and info->vsk */
>+static struct sk_buff *
>+virtio_transport_sock_alloc_send_skb(struct virtio_vsock_pkt_info *info, unsigned int size,
>+				     gfp_t mask, int *err)
>+{
>+	struct sk_buff *skb;
>+	struct sock *sk;
>+	int noblock;
>+
>+	if (size < VIRTIO_VSOCK_SKB_HEADROOM) {
>+		*err = -EINVAL;

What about using ERR_PTR, instead of passing *err?

>+		return NULL;
>+	}
>+
>+	if (info->msg)
>+		noblock = info->msg->msg_flags & MSG_DONTWAIT;
>+	else
>+		noblock = 1;
>+
>+	sk = sk_vsock(info->vsk);
>+	sk->sk_allocation = mask;
>+	skb = sock_alloc_send_skb(sk, size, noblock, err);
>+	if (!skb)
>+		return NULL;
>+
>+	skb_reserve(skb, VIRTIO_VSOCK_SKB_HEADROOM);
>+	return skb;
>+}
>+
> /* Returns a new packet on success, otherwise returns NULL.
>  *
>  * If NULL is returned, errp is set to a negative errno.
>@@ -47,7 +76,8 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 			   u32 src_cid,
> 			   u32 src_port,
> 			   u32 dst_cid,
>-			   u32 dst_port)
>+			   u32 dst_port,
>+			   int *errp)
> {
> 	const size_t skb_len = VIRTIO_VSOCK_SKB_HEADROOM + len;
> 	struct virtio_vsock_hdr *hdr;
>@@ -55,9 +85,21 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 	void *payload;
> 	int err;
>
>-	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>-	if (!skb)
>+	/* dgrams do not use credits, self-throttle according to sk_sndbuf
>+	 * using sock_alloc_send_skb. This helps avoid triggering the OOM.
>+	 */
>+	if (info->vsk && info->type == VIRTIO_VSOCK_TYPE_DGRAM) {
>+		skb = virtio_transport_sock_alloc_send_skb(info, skb_len, GFP_KERNEL, &err);
>+	} else {
>+		skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
>+		if (!skb)
>+			err = -ENOMEM;
>+	}
>+
>+	if (!skb) {
>+		*errp = err;
> 		return NULL;
>+	}
>
> 	hdr = virtio_vsock_hdr(skb);
> 	hdr->type	= cpu_to_le16(info->type);
>@@ -102,6 +144,7 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 	return skb;
>
> out:
>+	*errp = err;
> 	kfree_skb(skb);
> 	return NULL;
> }
>@@ -183,7 +226,9 @@ EXPORT_SYMBOL_GPL(virtio_transport_deliver_tap_pkt);
>
> static u16 virtio_transport_get_type(struct sock *sk)
> {
>-	if (sk->sk_type == SOCK_STREAM)
>+	if (sk->sk_type == SOCK_DGRAM)
>+		return VIRTIO_VSOCK_TYPE_DGRAM;
>+	else if (sk->sk_type == SOCK_STREAM)
> 		return VIRTIO_VSOCK_TYPE_STREAM;
> 	else
> 		return VIRTIO_VSOCK_TYPE_SEQPACKET;
>@@ -239,11 +284,10 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>
> 		skb = virtio_transport_alloc_skb(info, skb_len,
> 						 src_cid, src_port,
>-						 dst_cid, dst_port);
>-		if (!skb) {
>-			ret = -ENOMEM;
>+						 dst_cid, dst_port,
>+						 &ret);
>+		if (!skb)
> 			break;
>-		}
>
> 		virtio_transport_inc_tx_pkt(vvs, skb);
>
>@@ -588,7 +632,56 @@ virtio_transport_dgram_dequeue(struct vsock_sock *vsk,
> 			       struct msghdr *msg,
> 			       size_t len, int flags)
> {
>-	return -EOPNOTSUPP;
>+	struct sk_buff *skb;
>+	struct sock *sk;
>+	size_t bytes;
>+	int err;
>+
>+	if (flags & MSG_OOB || flags & MSG_ERRQUEUE)
>+		return -EOPNOTSUPP;
>+
>+	sk = sk_vsock(vsk);
>+	err = 0;
>+
>+	skb = skb_recv_datagram(sk, flags, &err);
>+	if (!skb)
>+		goto out;
>+
>+	/* If the user buffer is too short then truncate the message and set
>+	 * MSG_TRUNC. The remainder will be discarded when the skb is freed.
>+	 */
>+	if (len < skb->len) {
>+		bytes = len;
>+		msg->msg_flags |= MSG_TRUNC;
>+	} else {
>+		bytes = skb->len;
>+	}
>+
>+	/* Copy to msg from skb->data.
>+	 * virtio_vsock_alloc_skb() should have already set
>+	 * the skb pointers correctly. That is, skb->data
>+	 * should not still be at skb->head.
>+	 */
>+	WARN_ON(skb->data == skb->head);
>+	err = skb_copy_datagram_msg(skb, 0, msg, bytes);
>+	if (err)
>+		goto out;
>+
>+	/* On success, return the number bytes copied to the user buffer */
>+	err = bytes;
>+
>+	if (msg->msg_name) {
>+		/* Provide the address of the sender. */
>+		DECLARE_SOCKADDR(struct sockaddr_vm *, vm_addr, msg->msg_name);
>+
>+		vsock_addr_init(vm_addr, le64_to_cpu(virtio_vsock_hdr(skb)->src_cid),
>+				le32_to_cpu(virtio_vsock_hdr(skb)->src_port));
>+		msg->msg_namelen = sizeof(*vm_addr);
>+	}
>+
>+out:
>+	skb_free_datagram(&vsk->sk, skb);
>+	return err;
> }
> EXPORT_SYMBOL_GPL(virtio_transport_dgram_dequeue);
>
>@@ -793,13 +886,13 @@ EXPORT_SYMBOL_GPL(virtio_transport_stream_allow);
> int virtio_transport_dgram_bind(struct vsock_sock *vsk,
> 				struct sockaddr_vm *addr)
> {
>-	return -EOPNOTSUPP;
>+	return vsock_bind_stream(vsk, addr);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_dgram_bind);
>
> bool virtio_transport_dgram_allow(u32 cid, u32 port)
> {
>-	return false;
>+	return true;

Should we check if F_DGRAM is negotiated?

> }
> EXPORT_SYMBOL_GPL(virtio_transport_dgram_allow);
>
>@@ -835,7 +928,37 @@ 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,
>+		.vsk = vsk,
>+		.type = VIRTIO_VSOCK_TYPE_DGRAM,
>+	};
>+	const struct virtio_transport *t_ops;
>+	u32 src_cid, src_port;
>+	struct sk_buff *skb;
>+	int err;
>+
>+	if (dgram_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
>+		return -EMSGSIZE;
>+
>+	t_ops = virtio_transport_get_ops(vsk);
>+	if (unlikely(!t_ops))
>+		return -EFAULT;
>+
>+	src_cid = t_ops->transport.get_local_cid();
>+	src_port = vsk->local_addr.svm_port;
>+
>+	skb = virtio_transport_alloc_skb(&info, dgram_len,
>+					 src_cid, src_port,
>+					 remote_addr->svm_cid,
>+					 remote_addr->svm_port,
>+					 &err);
>+
>+	if (!skb)
>+		return err;
>+
>+	return t_ops->send_pkt(skb);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_dgram_enqueue);
>
>@@ -892,6 +1015,7 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
> 		.reply = true,
> 	};
> 	struct sk_buff *reply;
>+	int err;
>
> 	/* Send RST only if the original pkt is not a RST pkt */
> 	if (le16_to_cpu(hdr->op) == VIRTIO_VSOCK_OP_RST)
>@@ -904,9 +1028,10 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
> 					   le64_to_cpu(hdr->dst_cid),
> 					   le32_to_cpu(hdr->dst_port),
> 					   le64_to_cpu(hdr->src_cid),
>-					   le32_to_cpu(hdr->src_port));
>+					   le32_to_cpu(hdr->src_port),
>+					   &err);
> 	if (!reply)
>-		return -ENOMEM;
>+		return err;
>
> 	return t->send_pkt(reply);
> }
>@@ -1126,6 +1251,25 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> 		kfree_skb(skb);
> }
>
>+/* This function takes ownership of the skb.
>+ *
>+ * It either places the skb on the sk_receive_queue or frees it.
>+ */
>+static int
>+virtio_transport_recv_dgram(struct sock *sk, struct sk_buff *skb)

We don't use the return value, so this can be void.

>+{
>+	int err;
>+
>+	err = sock_queue_rcv_skb(sk, skb);
>+	if (err < 0) {
>+		kfree_skb(skb);
>+		return err;
>+	}
>+
>+	sk->sk_data_ready(sk);
>+	return 0;
>+}
>+
> static int
> virtio_transport_recv_connected(struct sock *sk,
> 				struct sk_buff *skb)
>@@ -1289,7 +1433,8 @@ 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
>@@ -1303,22 +1448,25 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> 	struct vsock_sock *vsk;
> 	struct sock *sk;
> 	bool space_available;
>+	u16 type;
>
> 	vsock_addr_init(&src, le64_to_cpu(hdr->src_cid),
> 			le32_to_cpu(hdr->src_port));
> 	vsock_addr_init(&dst, le64_to_cpu(hdr->dst_cid),
> 			le32_to_cpu(hdr->dst_port));
>
>+	type = le16_to_cpu(hdr->type);
>+
> 	trace_virtio_transport_recv_pkt(src.svm_cid, src.svm_port,
> 					dst.svm_cid, dst.svm_port,
> 					le32_to_cpu(hdr->len),
>-					le16_to_cpu(hdr->type),
>+					type,
> 					le16_to_cpu(hdr->op),
> 					le32_to_cpu(hdr->flags),
> 					le32_to_cpu(hdr->buf_alloc),
> 					le32_to_cpu(hdr->fwd_cnt));
>
>-	if (!virtio_transport_valid_type(le16_to_cpu(hdr->type))) {
>+	if (!virtio_transport_valid_type(type)) {
> 		(void)virtio_transport_reset_no_sock(t, skb);
> 		goto free_pkt;
> 	}
>@@ -1330,13 +1478,15 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> 	if (!sk) {
> 		sk = vsock_find_bound_socket(&dst);
> 		if (!sk) {
>-			(void)virtio_transport_reset_no_sock(t, skb);
>+			if (type != VIRTIO_VSOCK_TYPE_DGRAM)
>+				(void)virtio_transport_reset_no_sock(t, skb);
> 			goto free_pkt;
> 		}
> 	}
>
>-	if (virtio_transport_get_type(sk) != le16_to_cpu(hdr->type)) {
>-		(void)virtio_transport_reset_no_sock(t, skb);
>+	if (virtio_transport_get_type(sk) != type) {
>+		if (type != VIRTIO_VSOCK_TYPE_DGRAM)
>+			(void)virtio_transport_reset_no_sock(t, skb);
> 		sock_put(sk);
> 		goto free_pkt;
> 	}
>@@ -1352,12 +1502,18 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
>
> 	/* Check if sk has been closed before lock_sock */
> 	if (sock_flag(sk, SOCK_DONE)) {
>-		(void)virtio_transport_reset_no_sock(t, skb);
>+		if (type != VIRTIO_VSOCK_TYPE_DGRAM)
>+			(void)virtio_transport_reset_no_sock(t, skb);
> 		release_sock(sk);
> 		sock_put(sk);
> 		goto free_pkt;
> 	}
>
>+	if (sk->sk_type == SOCK_DGRAM) {
>+		virtio_transport_recv_dgram(sk, skb);
>+		goto out;
>+	}
>+
> 	space_available = virtio_transport_space_update(sk, skb);
>
> 	/* Update CID in case it has changed after a transport reset event */
>@@ -1389,6 +1545,7 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> 		break;
> 	}
>
>+out:
> 	release_sock(sk);
>
> 	/* Release refcnt obtained when we fetched this socket out of the
>
>-- 
>2.30.2
>

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