Re: [PATCH v2] vsock: replace virtio_vsock_pkt with sk_buff

[Stefano Garzarella]

On Wed, Oct 05, 2022 at 06:19:44PM -0700, Bobby Eshleman wrote:
> This patch replaces the struct virtio_vsock_pkt with struct sk_buff.
>
> Using sk_buff in vsock benefits it by a) allowing vsock to be extended
> for socket-related features like sockmap, b) vsock may in the future
> use other sk_buff-dependent kernel capabilities, and c) vsock shares
> commonality with other socket types.
>
> This patch is taken from the original series found here:
> https://lore.kernel.org/all/cover.1660362668.git.bobby.eshleman@xxxxxxxxxxxxx/
>
> Small-sized packet throughput improved by ~5% (from 18.53 Mb/s to 19.51
> Mb/s). Tested using uperf, 16B payloads, 64 threads, 100s, averaged from
> 10 test runs (n=10). This improvement is likely due to packet merging.
>
> Large-sized packet throughput decreases ~9% (from 27.25 Gb/s to 25.04
> Gb/s). Tested using uperf, 64KB payloads, 64 threads, 100s, averaged
> from 10 test runs (n=10).
>
> Medium-sized packet throughput decreases ~5% (from 4.0 Gb/s to 3.81
> Gb/s). Tested using uperf, 4k to 8k payload sizes picked randomly
> according to normal distribution, 64 threads, 100s, averaged from 10
> test runs (n=10).
>
> All tests done in nested VMs (virtual host and virtual guest).
>
> Signed-off-by: Bobby Eshleman <bobby.eshleman@xxxxxxxxxxxxx>
> ---
> Changes in v2:
> - Use alloc_skb() directly instead of sock_alloc_send_pskb() to minimize
>  uAPI changes.
> - Do not marshal errors to -ENOMEM for non-virtio implementations.
> - No longer a part of the original series
> - Some code cleanup and refactoring
> - Include performance stats
>
> drivers/vhost/vsock.c                   | 215 +++++------
> include/linux/virtio_vsock.h            |  64 +++-
> net/vmw_vsock/af_vsock.c                |   1 +
> net/vmw_vsock/virtio_transport.c        | 206 +++++-----
> net/vmw_vsock/virtio_transport_common.c | 483 ++++++++++++------------
> net/vmw_vsock/vsock_loopback.c          |  51 +--
> 6 files changed, 504 insertions(+), 516 deletions(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index 368330417bde..6179e637602f 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -51,8 +51,7 @@ struct vhost_vsock {
> 	struct hlist_node hash;
>
> 	struct vhost_work send_pkt_work;
> -	spinlock_t send_pkt_list_lock;
> -	struct list_head send_pkt_list;	/* host->guest pending packets */
> +	struct sk_buff_head send_pkt_queue; /* host->guest pending packets */
>
> 	atomic_t queued_replies;
>
> @@ -108,7 +107,8 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 	vhost_disable_notify(&vsock->dev, vq);
>
> 	do {
> -		struct virtio_vsock_pkt *pkt;
> +		struct sk_buff *skb;
> +		struct virtio_vsock_hdr *hdr;

Reverse xmas tree is preferred in the net tree.
https://docs.kernel.org/process/maintainer-netdev.html?highlight=what+reverse+xmas+tree#what-is-reverse-xmas-tree

Please, check also in other places in this patch.

> 		struct iov_iter iov_iter;
> 		unsigned out, in;
> 		size_t nbytes;
> @@ -116,31 +116,22 @@ vhost_transport_do_send_pkt(struct vhost_vsock 
> *vsock,
> 		int head;
> 		u32 flags_to_restore = 0;
>
> -		spin_lock_bh(&vsock->send_pkt_list_lock);
> -		if (list_empty(&vsock->send_pkt_list)) {
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +		skb = skb_dequeue(&vsock->send_pkt_queue);
> +
> +		if (!skb) {
> 			vhost_enable_notify(&vsock->dev, vq);
> 			break;
> 		}
>
> -		pkt = list_first_entry(&vsock->send_pkt_list,
> -				       struct virtio_vsock_pkt, list);
> -		list_del_init(&pkt->list);
> -		spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> 		head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
> 					 &out, &in, NULL, NULL);
> 		if (head < 0) {
> -			spin_lock_bh(&vsock->send_pkt_list_lock);
> -			list_add(&pkt->list, &vsock->send_pkt_list);
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +			skb_queue_head(&vsock->send_pkt_queue, skb);
> 			break;
> 		}
>
> 		if (head == vq->num) {
> -			spin_lock_bh(&vsock->send_pkt_list_lock);
> -			list_add(&pkt->list, &vsock->send_pkt_list);
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +			skb_queue_head(&vsock->send_pkt_queue, skb);
>
> 			/* We cannot finish yet if more buffers snuck in while
> 			 * re-enabling notify.
> @@ -153,26 +144,27 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 		}
>
> 		if (out) {
> -			virtio_transport_free_pkt(pkt);
> +			kfree_skb(skb);
> 			vq_err(vq, "Expected 0 output buffers, got %u\n", out);
> 			break;
> 		}
>
> 		iov_len = iov_length(&vq->iov[out], in);
> -		if (iov_len < sizeof(pkt->hdr)) {
> -			virtio_transport_free_pkt(pkt);
> +		if (iov_len < sizeof(*hdr)) {
> +			kfree_skb(skb);
> 			vq_err(vq, "Buffer len [%zu] too small\n", 
> 			iov_len);
> 			break;
> 		}
>
> 		iov_iter_init(&iov_iter, READ, &vq->iov[out], in, iov_len);
> -		payload_len = pkt->len - pkt->off;
> +		payload_len = skb->len - vsock_metadata(skb)->off;

I guess the compiler will optimize, but what about store the metadata 
pointer in a variable?

> +		hdr = vsock_hdr(skb);
>
> 		/* If the packet is greater than the space available in the
> 		 * buffer, we split it using multiple buffers.
> 		 */
> -		if (payload_len > iov_len - sizeof(pkt->hdr)) {
> -			payload_len = iov_len - sizeof(pkt->hdr);
> +		if (payload_len > iov_len - sizeof(*hdr)) {
> +			payload_len = iov_len - sizeof(*hdr);
>
> 			/* As we are copying pieces of large packet's buffer to
> 			 * small rx buffers, headers of packets in rx queue are
> @@ -185,31 +177,31 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 			 * bits set. After initialized header will be copied to
> 			 * rx buffer, these required bits will be restored.
> 			 */
> -			if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM) {
> -				pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
> +			if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) {
> +				hdr->flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
> 				flags_to_restore |= VIRTIO_VSOCK_SEQ_EOM;
>
> -				if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR) {
> -					pkt->hdr.flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
> +				if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOR) {
> +					hdr->flags &= ~cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
> 					flags_to_restore |= VIRTIO_VSOCK_SEQ_EOR;
> 				}
> 			}
> 		}
>
> 		/* Set the correct length in the header */
> -		pkt->hdr.len = cpu_to_le32(payload_len);
> +		hdr->len = cpu_to_le32(payload_len);
>
> -		nbytes = copy_to_iter(&pkt->hdr, sizeof(pkt->hdr), &iov_iter);
> -		if (nbytes != sizeof(pkt->hdr)) {
> -			virtio_transport_free_pkt(pkt);
> +		nbytes = copy_to_iter(hdr, sizeof(*hdr), &iov_iter);
> +		if (nbytes != sizeof(*hdr)) {
> +			kfree_skb(skb);
> 			vq_err(vq, "Faulted on copying pkt hdr\n");
> 			break;
> 		}
>
> -		nbytes = copy_to_iter(pkt->buf + pkt->off, payload_len,
> +		nbytes = copy_to_iter(skb->data + vsock_metadata(skb)->off, payload_len,
> 				      &iov_iter);
> 		if (nbytes != payload_len) {
> -			virtio_transport_free_pkt(pkt);
> +			kfree_skb(skb);
> 			vq_err(vq, "Faulted on copying pkt buf\n");
> 			break;
> 		}
> @@ -217,31 +209,28 @@ vhost_transport_do_send_pkt(struct vhost_vsock 
> *vsock,
> 		/* Deliver to monitoring devices all packets that we
> 		 * will transmit.
> 		 */
> -		virtio_transport_deliver_tap_pkt(pkt);
> +		virtio_transport_deliver_tap_pkt(skb);
>
> -		vhost_add_used(vq, head, sizeof(pkt->hdr) + payload_len);
> +		vhost_add_used(vq, head, sizeof(*hdr) + payload_len);
> 		added = true;
>
> -		pkt->off += payload_len;
> +		vsock_metadata(skb)->off += payload_len;
> 		total_len += payload_len;
>
> 		/* If we didn't send all the payload we can requeue the packet
> 		 * to send it with the next available buffer.
> 		 */
> -		if (pkt->off < pkt->len) {
> -			pkt->hdr.flags |= cpu_to_le32(flags_to_restore);
> +		if (vsock_metadata(skb)->off < skb->len) {
> +			hdr->flags |= cpu_to_le32(flags_to_restore);
>
> -			/* We are queueing the same virtio_vsock_pkt to handle
> +			/* We are queueing the same skb to handle
> 			 * the remaining bytes, and we want to deliver it
> 			 * to monitoring devices in the next iteration.
> 			 */
> -			pkt->tap_delivered = false;
> -
> -			spin_lock_bh(&vsock->send_pkt_list_lock);
> -			list_add(&pkt->list, &vsock->send_pkt_list);
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +			vsock_metadata(skb)->flags &= ~VIRTIO_VSOCK_METADATA_FLAGS_TAP_DELIVERED;
> +			skb_queue_head(&vsock->send_pkt_queue, skb);
> 		} else {
> -			if (pkt->reply) {
> +			if (vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_REPLY) {
> 				int val;
>
> 				val = atomic_dec_return(&vsock->queued_replies);
> @@ -253,7 +242,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> 					restart_tx = true;
> 			}
>
> -			virtio_transport_free_pkt(pkt);
> +			consume_skb(skb);
> 		}
> 	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
> 	if (added)
> @@ -278,28 +267,26 @@ static void vhost_transport_send_pkt_work(struct vhost_work *work)
> }
>
> static int
> -vhost_transport_send_pkt(struct virtio_vsock_pkt *pkt)
> +vhost_transport_send_pkt(struct sk_buff *skb)
> {
> 	struct vhost_vsock *vsock;
> -	int len = pkt->len;
> +	int len = skb->len;
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
>
> 	rcu_read_lock();
>
> 	/* Find the vhost_vsock according to guest context id  */
> -	vsock = vhost_vsock_get(le64_to_cpu(pkt->hdr.dst_cid));
> +	vsock = vhost_vsock_get(le64_to_cpu(hdr->dst_cid));
> 	if (!vsock) {
> 		rcu_read_unlock();
> -		virtio_transport_free_pkt(pkt);
> +		kfree_skb(skb);
> 		return -ENODEV;
> 	}
>
> -	if (pkt->reply)
> +	if (vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_REPLY)
> 		atomic_inc(&vsock->queued_replies);
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	list_add_tail(&pkt->list, &vsock->send_pkt_list);
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> +	skb_queue_tail(&vsock->send_pkt_queue, skb);
> 	vhost_work_queue(&vsock->dev, &vsock->send_pkt_work);
>
> 	rcu_read_unlock();
> @@ -310,10 +297,8 @@ static int
> vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> {
> 	struct vhost_vsock *vsock;
> -	struct virtio_vsock_pkt *pkt, *n;
> 	int cnt = 0;
> 	int ret = -ENODEV;
> -	LIST_HEAD(freeme);
>
> 	rcu_read_lock();
>
> @@ -322,20 +307,7 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> 	if (!vsock)
> 		goto out;
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	list_for_each_entry_safe(pkt, n, &vsock->send_pkt_list, list) {
> -		if (pkt->vsk != vsk)
> -			continue;
> -		list_move(&pkt->list, &freeme);
> -	}
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> -	list_for_each_entry_safe(pkt, n, &freeme, list) {
> -		if (pkt->reply)
> -			cnt++;
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> +	cnt = virtio_transport_purge_skbs(vsk, &vsock->send_pkt_queue);
>
> 	if (cnt) {
> 		struct vhost_virtqueue *tx_vq = &vsock->vqs[VSOCK_VQ_TX];
> @@ -352,11 +324,12 @@ vhost_transport_cancel_pkt(struct vsock_sock *vsk)
> 	return ret;
> }
>
> -static struct virtio_vsock_pkt *
> -vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
> +static struct sk_buff *
> +vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
> 		      unsigned int out, unsigned int in)
> {
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> +	struct virtio_vsock_hdr *hdr;
> 	struct iov_iter iov_iter;
> 	size_t nbytes;
> 	size_t len;
> @@ -366,50 +339,50 @@ vhost_vsock_alloc_pkt(struct vhost_virtqueue *vq,
> 		return NULL;
> 	}
>
> -	pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
> -	if (!pkt)
> +	len = iov_length(vq->iov, out);
> +
> +	/* len contains both payload and hdr, so only add additional space for metadata */
> +	skb = alloc_skb(len + sizeof(struct virtio_vsock_metadata), GFP_KERNEL);
> +	if (!skb)
> 		return NULL;
>
> -	len = iov_length(vq->iov, out);
> +	/* Only zero metadata, preserve the header */
> +	memset(skb->head, 0, sizeof(struct virtio_vsock_metadata));
> +	virtio_vsock_skb_reserve(skb);
> 	iov_iter_init(&iov_iter, WRITE, vq->iov, out, len);
>
> -	nbytes = copy_from_iter(&pkt->hdr, sizeof(pkt->hdr), &iov_iter);
> -	if (nbytes != sizeof(pkt->hdr)) {
> +	hdr = vsock_hdr(skb);
> +	nbytes = copy_from_iter(hdr, sizeof(*hdr), &iov_iter);
> +	if (nbytes != sizeof(*hdr)) {
> 		vq_err(vq, "Expected %zu bytes for pkt->hdr, got %zu bytes\n",
> -		       sizeof(pkt->hdr), nbytes);
> -		kfree(pkt);
> +		       sizeof(*hdr), nbytes);
> +		kfree_skb(skb);
> 		return NULL;
> 	}
>
> -	pkt->len = le32_to_cpu(pkt->hdr.len);
> +	len = le32_to_cpu(hdr->len);
>
> 	/* No payload */
> -	if (!pkt->len)
> -		return pkt;
> +	if (!len)
> +		return skb;
>
> 	/* The pkt is too big */
> -	if (pkt->len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> -		kfree(pkt);
> +	if (len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> +		kfree_skb(skb);
> 		return NULL;
> 	}
>
> -	pkt->buf = kmalloc(pkt->len, GFP_KERNEL);
> -	if (!pkt->buf) {
> -		kfree(pkt);
> -		return NULL;
> -	}
> +	virtio_vsock_skb_rx_put(skb);
>
> -	pkt->buf_len = pkt->len;
> -
> -	nbytes = copy_from_iter(pkt->buf, pkt->len, &iov_iter);
> -	if (nbytes != pkt->len) {
> -		vq_err(vq, "Expected %u byte payload, got %zu bytes\n",
> -		       pkt->len, nbytes);
> -		virtio_transport_free_pkt(pkt);
> +	nbytes = copy_from_iter(skb->data, len, &iov_iter);
> +	if (nbytes != len) {
> +		vq_err(vq, "Expected %zu byte payload, got %zu bytes\n",
> +		       len, nbytes);
> +		kfree_skb(skb);
> 		return NULL;
> 	}
>
> -	return pkt;
> +	return skb;
> }
>
> /* Is there space left for replies to rx packets? */
> @@ -496,7 +469,7 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
> 						  poll.work);
> 	struct vhost_vsock *vsock = container_of(vq->dev, struct vhost_vsock,
> 						 dev);
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> 	int head, pkts = 0, total_len = 0;
> 	unsigned int out, in;
> 	bool added = false;
> @@ -511,6 +484,9 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
>
> 	vhost_disable_notify(&vsock->dev, vq);
> 	do {
> +		struct virtio_vsock_hdr *hdr;
> +		u32 len;
> +
> 		if (!vhost_vsock_more_replies(vsock)) {
> 			/* Stop tx until the device processes already
> 			 * pending replies.  Leave tx virtqueue
> @@ -532,26 +508,29 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
> 			break;
> 		}
>
> -		pkt = vhost_vsock_alloc_pkt(vq, out, in);
> -		if (!pkt) {
> -			vq_err(vq, "Faulted on pkt\n");
> +		skb = vhost_vsock_alloc_skb(vq, out, in);
> +		if (!skb)
> 			continue;
> -		}
>
> -		total_len += sizeof(pkt->hdr) + pkt->len;
> +		len = skb->len;
>
> 		/* Deliver to monitoring devices all received packets */
> -		virtio_transport_deliver_tap_pkt(pkt);
> +		virtio_transport_deliver_tap_pkt(skb);
> +
> +		hdr = vsock_hdr(skb);
>
> 		/* Only accept correctly addressed packets */
> -		if (le64_to_cpu(pkt->hdr.src_cid) == vsock->guest_cid &&
> -		    le64_to_cpu(pkt->hdr.dst_cid) ==
> +		if (le64_to_cpu(hdr->src_cid) == vsock->guest_cid &&
> +		    le64_to_cpu(hdr->dst_cid) ==
> 		    vhost_transport_get_local_cid())
> -			virtio_transport_recv_pkt(&vhost_transport, pkt);
> +			virtio_transport_recv_pkt(&vhost_transport, skb);
> 		else
> -			virtio_transport_free_pkt(pkt);
> +			kfree_skb(skb);
> +
>
> -		vhost_add_used(vq, head, 0);
> +		len += sizeof(*hdr);
> +		vhost_add_used(vq, head, len);

Please don't use `len` in vhost_add_used(). We should pass the number of 
bytes written by the device. Take a look at 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=49d8c5ffad07ca014cfae72a1b9b8c52b6ad9cb8

Maybe we should document better vhost_add_used() to avoid future issue.

> +		total_len += len;
> 		added = true;
> 	} while(likely(!vhost_exceeds_weight(vq, ++pkts, total_len)));
>
> @@ -693,8 +672,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
> 		       VHOST_VSOCK_WEIGHT, true, NULL);
>
> 	file->private_data = vsock;
> -	spin_lock_init(&vsock->send_pkt_list_lock);
> -	INIT_LIST_HEAD(&vsock->send_pkt_list);
> +	skb_queue_head_init(&vsock->send_pkt_queue);
> 	vhost_work_init(&vsock->send_pkt_work, vhost_transport_send_pkt_work);
> 	return 0;
>
> @@ -760,16 +738,7 @@ static int vhost_vsock_dev_release(struct inode *inode, struct file *file)
> 	vhost_vsock_flush(vsock);
> 	vhost_dev_stop(&vsock->dev);
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	while (!list_empty(&vsock->send_pkt_list)) {
> -		struct virtio_vsock_pkt *pkt;
> -
> -		pkt = list_first_entry(&vsock->send_pkt_list,
> -				struct virtio_vsock_pkt, list);
> -		list_del_init(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> +	skb_queue_purge(&vsock->send_pkt_queue);
>
> 	vhost_dev_cleanup(&vsock->dev);
> 	kfree(vsock->dev.vqs);
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 35d7eedb5e8e..b1dff55c91a5 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -4,9 +4,47 @@
>
> #include <uapi/linux/virtio_vsock.h>
> #include <linux/socket.h>
> +#include <vdso/bits.h>
> #include <net/sock.h>
> #include <net/af_vsock.h>
>
> +/* Threshold for detecting small packets to copy */
> +#define GOOD_COPY_LEN  128

Since we moved this in an header, I guess is better to add a prefix 
(e.g. VIRTIO_VSOCK_GOOD_COPY_LEN)

> +
> +enum virtio_vsock_metadata_flags {
> +	VIRTIO_VSOCK_METADATA_FLAGS_REPLY		= BIT(0),
> +	VIRTIO_VSOCK_METADATA_FLAGS_TAP_DELIVERED	= BIT(1),
> +};
> +
> +/* Used only by the virtio/vhost vsock drivers, not related to protocol */
> +struct virtio_vsock_metadata {
> +	size_t off;
> +	enum virtio_vsock_metadata_flags flags;
> +};
> +
> +#define vsock_hdr(skb) \

For uniformity better virtio_vsock_get_hdr()

> +	((struct virtio_vsock_hdr *) \
> +	 ((void *)skb->head + sizeof(struct virtio_vsock_metadata)))
> +
> +#define vsock_metadata(skb) \

Ditto

> +	((struct virtio_vsock_metadata *)skb->head)
> +
> +#define VIRTIO_VSOCK_SKB_RESERVE_SIZE \
> +	(sizeof(struct virtio_vsock_metadata) + sizeof(struct virtio_vsock_hdr))
> +
> +#define virtio_vsock_skb_reserve(skb) \
> +	skb_reserve(skb, VIRTIO_VSOCK_SKB_RESERVE_SIZE)
> +
> +static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
> +{
> +	u32 len;
> +
> +	len = le32_to_cpu(vsock_hdr(skb)->len);
> +
> +	if (len > 0)
> +		skb_put(skb, len);
> +}
> +
> #define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
> #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
> #define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
> @@ -35,23 +73,10 @@ struct virtio_vsock_sock {
> 	u32 last_fwd_cnt;
> 	u32 rx_bytes;
> 	u32 buf_alloc;
> -	struct list_head rx_queue;
> +	struct sk_buff_head rx_queue;
> 	u32 msg_count;
> };
>
> -struct virtio_vsock_pkt {
> -	struct virtio_vsock_hdr	hdr;
> -	struct list_head list;
> -	/* socket refcnt not held, only use for cancellation */
> -	struct vsock_sock *vsk;
> -	void *buf;
> -	u32 buf_len;
> -	u32 len;
> -	u32 off;
> -	bool reply;
> -	bool tap_delivered;
> -};
> -
> struct virtio_vsock_pkt_info {
> 	u32 remote_cid, remote_port;
> 	struct vsock_sock *vsk;
> @@ -68,7 +93,7 @@ struct virtio_transport {
> 	struct vsock_transport transport;
>
> 	/* Takes ownership of the packet */
> -	int (*send_pkt)(struct virtio_vsock_pkt *pkt);
> +	int (*send_pkt)(struct sk_buff *skb);
> };
>
> ssize_t
> @@ -149,11 +174,10 @@ virtio_transport_dgram_enqueue(struct vsock_sock *vsk,
> void virtio_transport_destruct(struct vsock_sock *vsk);
>
> void virtio_transport_recv_pkt(struct virtio_transport *t,
> -			       struct virtio_vsock_pkt *pkt);
> -void virtio_transport_free_pkt(struct virtio_vsock_pkt *pkt);
> -void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt);
> +			       struct sk_buff *skb);
> +void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct sk_buff *skb);
> u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 wanted);
> void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
> -void virtio_transport_deliver_tap_pkt(struct virtio_vsock_pkt *pkt);
> -
> +void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
> +int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *queue);
> #endif /* _LINUX_VIRTIO_VSOCK_H */
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index b4ee163154a6..de8a9b0ec3a0 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -748,6 +748,7 @@ static struct sock *__vsock_create(struct net *net,
> 	vsock_addr_init(&vsk->local_addr, VMADDR_CID_ANY, VMADDR_PORT_ANY);
> 	vsock_addr_init(&vsk->remote_addr, VMADDR_CID_ANY, VMADDR_PORT_ANY);
>
> +	sk->sk_allocation = GFP_KERNEL;

This will change also other transports, like VMCI that uses sk_buff for 
datagram. We should check that it is okay for them.

> 	sk->sk_destruct = vsock_sk_destruct;
> 	sk->sk_backlog_rcv = vsock_queue_rcv_skb;
> 	sock_reset_flag(sk, SOCK_DONE);
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index ad64f403536a..ac8c7003835b 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -21,6 +21,11 @@
> #include <linux/mutex.h>
> #include <net/af_vsock.h>
>
> +#define VIRTIO_VSOCK_MAX_RX_HDR_PAYLOAD_SIZE	\
> +	(VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE \
> +		 - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) \
> +		 - VIRTIO_VSOCK_SKB_RESERVE_SIZE)
> +
> static struct workqueue_struct *virtio_vsock_workqueue;
> static struct virtio_vsock __rcu *the_virtio_vsock;
> static DEFINE_MUTEX(the_virtio_vsock_mutex); /* protects the_virtio_vsock */
> @@ -42,8 +47,7 @@ struct virtio_vsock {
> 	bool tx_run;
>
> 	struct work_struct send_pkt_work;
> -	spinlock_t send_pkt_list_lock;
> -	struct list_head send_pkt_list;
> +	struct sk_buff_head send_pkt_queue;
>
> 	atomic_t queued_replies;
>
> @@ -101,41 +105,32 @@ virtio_transport_send_pkt_work(struct work_struct *work)
> 	vq = vsock->vqs[VSOCK_VQ_TX];
>
> 	for (;;) {
> -		struct virtio_vsock_pkt *pkt;
> +		struct sk_buff *skb;
> 		struct scatterlist hdr, buf, *sgs[2];
> 		int ret, in_sg = 0, out_sg = 0;
> 		bool reply;
>
> -		spin_lock_bh(&vsock->send_pkt_list_lock);
> -		if (list_empty(&vsock->send_pkt_list)) {
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> -			break;
> -		}
> +		skb = skb_dequeue(&vsock->send_pkt_queue);
>
> -		pkt = list_first_entry(&vsock->send_pkt_list,
> -				       struct virtio_vsock_pkt, list);
> -		list_del_init(&pkt->list);
> -		spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> -		virtio_transport_deliver_tap_pkt(pkt);
> +		if (!skb)
> +			break;
>
> -		reply = pkt->reply;
> +		virtio_transport_deliver_tap_pkt(skb);
> +		reply = vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_REPLY;
>
> -		sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
> +		sg_init_one(&hdr, vsock_hdr(skb), sizeof(*vsock_hdr(skb)));
> 		sgs[out_sg++] = &hdr;
> -		if (pkt->buf) {
> -			sg_init_one(&buf, pkt->buf, pkt->len);
> +		if (skb->len > 0) {
> +			sg_init_one(&buf, skb->data, skb->len);
> 			sgs[out_sg++] = &buf;
> 		}
>
> -		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, pkt, GFP_KERNEL);
> +		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
> 		/* Usually this means that there is no more space available in
> 		 * the vq
> 		 */
> 		if (ret < 0) {
> -			spin_lock_bh(&vsock->send_pkt_list_lock);
> -			list_add(&pkt->list, &vsock->send_pkt_list);
> -			spin_unlock_bh(&vsock->send_pkt_list_lock);
> +			skb_queue_head(&vsock->send_pkt_queue, skb);
> 			break;
> 		}
>
> @@ -163,33 +158,83 @@ virtio_transport_send_pkt_work(struct work_struct *work)
> 		queue_work(virtio_vsock_workqueue, &vsock->rx_work);
> }
>
> +static inline bool
> +virtio_transport_skbs_can_merge(struct sk_buff *old, struct sk_buff *new)
> +{
> +	return (new->len < GOOD_COPY_LEN &&
> +		skb_tailroom(old) >= new->len &&
> +		vsock_hdr(new)->src_cid == vsock_hdr(old)->src_cid &&
> +		vsock_hdr(new)->dst_cid == vsock_hdr(old)->dst_cid &&
> +		vsock_hdr(new)->src_port == vsock_hdr(old)->src_port &&
> +		vsock_hdr(new)->dst_port == vsock_hdr(old)->dst_port &&

For these first fields perhaps we can use a memcmp.

Can we use a pointer to store the header pointers?

> +		vsock_hdr(new)->type == vsock_hdr(old)->type &&
> +		vsock_hdr(new)->flags == vsock_hdr(old)->flags &&
> +		le16_to_cpu(vsock_hdr(old)->op) == VIRTIO_VSOCK_OP_RW &&
> +		le16_to_cpu(vsock_hdr(new)->op) == VIRTIO_VSOCK_OP_RW);
> +}
> +
> +/* Add new sk_buff to queue.
> + *
> + * Merge the two most recent skbs together if possible.
> + */
> +static void
> +virtio_transport_add_to_queue(struct sk_buff_head *queue, struct sk_buff *new)
> +{
> +	struct sk_buff *old;
> +
> +	spin_lock_bh(&queue->lock);
> +	if (skb_queue_empty_lockless(queue)) {
> +		__skb_queue_tail(queue, new);
> +		goto out;
> +	}
> +
> +	old = skb_peek_tail(queue);
> +
> +	/* In order to reduce skb memory overhead, we merge new packets 
> with
> +	 * older packets if they pass virtio_transport_skbs_can_merge().
> +	 */
> +	if (!virtio_transport_skbs_can_merge(old, new)) {
> +		__skb_queue_tail(queue, new);
> +		goto out;
> +	}
> +
> +	memcpy(skb_put(old, new->len), new->data, new->len);

This extra copy (and maybe also the call to can_merge) could be 
responsible for the perf drop. I understand why we have it, though, you 
could give it a try by avoiding merging and see what happens to 
performance.

Maybe we can split this patch and move change in a separate patch of the 
same series, and in the cover report the performance result 
incrementally with only the first patch applied and with first and 
second.

> +	vsock_hdr(old)->len = cpu_to_le32(old->len);
> +	vsock_hdr(old)->buf_alloc = vsock_hdr(new)->buf_alloc;
> +	vsock_hdr(old)->fwd_cnt = vsock_hdr(new)->fwd_cnt;
> +	dev_kfree_skb_any(new);
> +
> +out:
> +	spin_unlock_bh(&queue->lock);
> +}
> +
> static int
> -virtio_transport_send_pkt(struct virtio_vsock_pkt *pkt)
> +virtio_transport_send_pkt(struct sk_buff *skb)
> {
> +	struct virtio_vsock_hdr *hdr;
> 	struct virtio_vsock *vsock;
> -	int len = pkt->len;
> +	int len = skb->len;
> +
> +	hdr = vsock_hdr(skb);
>
> 	rcu_read_lock();
> 	vsock = rcu_dereference(the_virtio_vsock);
> 	if (!vsock) {
> -		virtio_transport_free_pkt(pkt);
> +		kfree_skb(skb);
> 		len = -ENODEV;
> 		goto out_rcu;
> 	}
>
> -	if (le64_to_cpu(pkt->hdr.dst_cid) == vsock->guest_cid) {
> -		virtio_transport_free_pkt(pkt);
> +	if (le64_to_cpu(hdr->dst_cid) == vsock->guest_cid) {
> +		kfree_skb(skb);
> 		len = -ENODEV;
> 		goto out_rcu;
> 	}
>
> -	if (pkt->reply)
> +	if (vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_REPLY)
> 		atomic_inc(&vsock->queued_replies);
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	list_add_tail(&pkt->list, &vsock->send_pkt_list);
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> +	virtio_transport_add_to_queue(&vsock->send_pkt_queue, skb);
> 	queue_work(virtio_vsock_workqueue, &vsock->send_pkt_work);
>
> out_rcu:
> @@ -201,9 +246,7 @@ static int
> virtio_transport_cancel_pkt(struct vsock_sock *vsk)
> {
> 	struct virtio_vsock *vsock;
> -	struct virtio_vsock_pkt *pkt, *n;
> 	int cnt = 0, ret;
> -	LIST_HEAD(freeme);
>
> 	rcu_read_lock();
> 	vsock = rcu_dereference(the_virtio_vsock);
> @@ -212,20 +255,7 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
> 		goto out_rcu;
> 	}
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	list_for_each_entry_safe(pkt, n, &vsock->send_pkt_list, list) {
> -		if (pkt->vsk != vsk)
> -			continue;
> -		list_move(&pkt->list, &freeme);
> -	}
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> -
> -	list_for_each_entry_safe(pkt, n, &freeme, list) {
> -		if (pkt->reply)
> -			cnt++;
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> +	cnt = virtio_transport_purge_skbs(vsk, &vsock->send_pkt_queue);
>
> 	if (cnt) {
> 		struct virtqueue *rx_vq = vsock->vqs[VSOCK_VQ_RX];
> @@ -246,38 +276,32 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
>
> static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
> {
> -	int buf_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
> -	struct virtio_vsock_pkt *pkt;
> -	struct scatterlist hdr, buf, *sgs[2];
> +	struct scatterlist pkt, *sgs[1];
> 	struct virtqueue *vq;
> 	int ret;
>
> 	vq = vsock->vqs[VSOCK_VQ_RX];
>
> 	do {
> -		pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
> -		if (!pkt)
> -			break;
> +		struct sk_buff *skb;
> +		const size_t len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE -
> +				SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>
> -		pkt->buf = kmalloc(buf_len, GFP_KERNEL);
> -		if (!pkt->buf) {
> -			virtio_transport_free_pkt(pkt);
> +		skb = alloc_skb(len, GFP_KERNEL);
> +		if (!skb)
> 			break;
> -		}
>
> -		pkt->buf_len = buf_len;
> -		pkt->len = buf_len;
> +		memset(skb->head, 0, VIRTIO_VSOCK_SKB_RESERVE_SIZE);
>
> -		sg_init_one(&hdr, &pkt->hdr, sizeof(pkt->hdr));
> -		sgs[0] = &hdr;
> +		sg_init_one(&pkt, vsock_hdr(skb), VIRTIO_VSOCK_MAX_RX_HDR_PAYLOAD_SIZE);
> +		sgs[0] = &pkt;
>
> -		sg_init_one(&buf, pkt->buf, buf_len);
> -		sgs[1] = &buf;
> -		ret = virtqueue_add_sgs(vq, sgs, 0, 2, pkt, GFP_KERNEL);
> -		if (ret) {
> -			virtio_transport_free_pkt(pkt);
> +		ret = virtqueue_add_sgs(vq, sgs, 0, 1, skb, GFP_KERNEL);
> +		if (ret < 0) {
> +			kfree_skb(skb);
> 			break;
> 		}
> +
> 		vsock->rx_buf_nr++;
> 	} while (vq->num_free);
> 	if (vsock->rx_buf_nr > vsock->rx_buf_max_nr)
> @@ -299,12 +323,12 @@ static void virtio_transport_tx_work(struct work_struct *work)
> 		goto out;
>
> 	do {
> -		struct virtio_vsock_pkt *pkt;
> +		struct sk_buff *skb;
> 		unsigned int len;
>
> 		virtqueue_disable_cb(vq);
> -		while ((pkt = virtqueue_get_buf(vq, &len)) != NULL) {
> -			virtio_transport_free_pkt(pkt);
> +		while ((skb = virtqueue_get_buf(vq, &len)) != NULL) {
> +			consume_skb(skb);
> 			added = true;
> 		}
> 	} while (!virtqueue_enable_cb(vq));
> @@ -529,7 +553,7 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 	do {
> 		virtqueue_disable_cb(vq);
> 		for (;;) {
> -			struct virtio_vsock_pkt *pkt;
> +			struct sk_buff *skb;
> 			unsigned int len;
>
> 			if (!virtio_transport_more_replies(vsock)) {
> @@ -540,23 +564,23 @@ static void virtio_transport_rx_work(struct work_struct *work)
> 				goto out;
> 			}
>
> -			pkt = virtqueue_get_buf(vq, &len);
> -			if (!pkt) {
> +			skb = virtqueue_get_buf(vq, &len);
> +			if (!skb)
> 				break;
> -			}
>
> 			vsock->rx_buf_nr--;
>
> 			/* Drop short/long packets */
> -			if (unlikely(len < sizeof(pkt->hdr) ||
> -				     len > sizeof(pkt->hdr) + pkt->len)) {
> -				virtio_transport_free_pkt(pkt);
> +			if (unlikely(len < sizeof(struct virtio_vsock_hdr) ||
> +				     len > VIRTIO_VSOCK_MAX_RX_HDR_PAYLOAD_SIZE)) {
> +				kfree_skb(skb);
> 				continue;
> 			}
>
> -			pkt->len = len - sizeof(pkt->hdr);
> -			virtio_transport_deliver_tap_pkt(pkt);
> -			virtio_transport_recv_pkt(&virtio_transport, pkt);
> +			virtio_vsock_skb_reserve(skb);
> +			virtio_vsock_skb_rx_put(skb);
> +			virtio_transport_deliver_tap_pkt(skb);
> +			virtio_transport_recv_pkt(&virtio_transport, skb);
> 		}
> 	} while (!virtqueue_enable_cb(vq));
>
> @@ -610,7 +634,7 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
> static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
> {
> 	struct virtio_device *vdev = vsock->vdev;
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
>
> 	/* Reset all connected sockets when the VQs disappear */
> 	vsock_for_each_connected_socket(&virtio_transport.transport,
> @@ -637,23 +661,16 @@ static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
> 	virtio_reset_device(vdev);
>
> 	mutex_lock(&vsock->rx_lock);
> -	while ((pkt = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_RX])))
> -		virtio_transport_free_pkt(pkt);
> +	while ((skb = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_RX])))
> +		kfree_skb(skb);
> 	mutex_unlock(&vsock->rx_lock);
>
> 	mutex_lock(&vsock->tx_lock);
> -	while ((pkt = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_TX])))
> -		virtio_transport_free_pkt(pkt);
> +	while ((skb = virtqueue_detach_unused_buf(vsock->vqs[VSOCK_VQ_TX])))
> +		kfree_skb(skb);
> 	mutex_unlock(&vsock->tx_lock);
>
> -	spin_lock_bh(&vsock->send_pkt_list_lock);
> -	while (!list_empty(&vsock->send_pkt_list)) {
> -		pkt = list_first_entry(&vsock->send_pkt_list,
> -				       struct virtio_vsock_pkt, list);
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> -	spin_unlock_bh(&vsock->send_pkt_list_lock);
> +	skb_queue_purge(&vsock->send_pkt_queue);
>
> 	/* Delete virtqueues and flush outstanding callbacks if any */
> 	vdev->config->del_vqs(vdev);
> @@ -690,8 +707,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
> 	mutex_init(&vsock->tx_lock);
> 	mutex_init(&vsock->rx_lock);
> 	mutex_init(&vsock->event_lock);
> -	spin_lock_init(&vsock->send_pkt_list_lock);
> -	INIT_LIST_HEAD(&vsock->send_pkt_list);
> +	skb_queue_head_init(&vsock->send_pkt_queue);
> 	INIT_WORK(&vsock->rx_work, virtio_transport_rx_work);
> 	INIT_WORK(&vsock->tx_work, virtio_transport_tx_work);
> 	INIT_WORK(&vsock->event_work, virtio_transport_event_work);
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index ec2c2afbf0d0..19678bd45c23 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -23,9 +23,6 @@
> /* How long to wait for graceful shutdown of a connection */
> #define VSOCK_CLOSE_TIMEOUT (8 * HZ)
>
> -/* Threshold for detecting small packets to copy */
> -#define GOOD_COPY_LEN  128
> -
> static const struct virtio_transport *
> virtio_transport_get_ops(struct vsock_sock *vsk)
> {
> @@ -37,53 +34,64 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
> 	return container_of(t, struct virtio_transport, transport);
> }
>
> -static struct virtio_vsock_pkt *
> -virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
> +/* Returns a new packet on success, otherwise returns NULL.
> + *
> + * If NULL is returned, errp is set to a negative errno.
> + */
> +static struct sk_buff *
> +virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
> 			   size_t len,
> 			   u32 src_cid,
> 			   u32 src_port,
> 			   u32 dst_cid,
> -			   u32 dst_port)
> +			   u32 dst_port,
> +			   int *errp)
> {
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> +	struct virtio_vsock_hdr *hdr;
> +	void *payload;
> +	const size_t skb_len = VIRTIO_VSOCK_SKB_RESERVE_SIZE + len;
> 	int err;
>
> -	pkt = kzalloc(sizeof(*pkt), GFP_KERNEL);
> -	if (!pkt)
> +	skb = alloc_skb(skb_len, GFP_KERNEL);
> +	if (!skb) {
> +		*errp = -ENOMEM;
> 		return NULL;
> +	}
>
> -	pkt->hdr.type		= cpu_to_le16(info->type);
> -	pkt->hdr.op		= cpu_to_le16(info->op);
> -	pkt->hdr.src_cid	= cpu_to_le64(src_cid);
> -	pkt->hdr.dst_cid	= cpu_to_le64(dst_cid);
> -	pkt->hdr.src_port	= cpu_to_le32(src_port);
> -	pkt->hdr.dst_port	= cpu_to_le32(dst_port);
> -	pkt->hdr.flags		= cpu_to_le32(info->flags);
> -	pkt->len		= len;
> -	pkt->hdr.len		= cpu_to_le32(len);
> -	pkt->reply		= info->reply;
> -	pkt->vsk		= info->vsk;
> -
> -	if (info->msg && len > 0) {
> -		pkt->buf = kmalloc(len, GFP_KERNEL);
> -		if (!pkt->buf)
> -			goto out_pkt;
> +	memset(skb->head, 0, VIRTIO_VSOCK_SKB_RESERVE_SIZE);
> +	virtio_vsock_skb_reserve(skb);
> +	payload = skb_put(skb, len);
>
> -		pkt->buf_len = len;
> +	hdr = vsock_hdr(skb);
> +	hdr->type	= cpu_to_le16(info->type);
> +	hdr->op		= cpu_to_le16(info->op);
> +	hdr->src_cid	= cpu_to_le64(src_cid);
> +	hdr->dst_cid	= cpu_to_le64(dst_cid);
> +	hdr->src_port	= cpu_to_le32(src_port);
> +	hdr->dst_port	= cpu_to_le32(dst_port);
> +	hdr->flags	= cpu_to_le32(info->flags);
> +	hdr->len	= cpu_to_le32(len);
>
> -		err = memcpy_from_msg(pkt->buf, info->msg, len);
> -		if (err)
> +	if (info->msg && len > 0) {
> +		err = memcpy_from_msg(payload, info->msg, len);
> +		if (err) {
> +			*errp = -ENOMEM;
> 			goto out;
> +		}
>
> 		if (msg_data_left(info->msg) == 0 &&
> 		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
> -			pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
> +			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
>
> 			if (info->msg->msg_flags & MSG_EOR)
> -				pkt->hdr.flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
> +				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
> 		}
> 	}
>
> +	if (info->reply)
> +		vsock_metadata(skb)->flags |= VIRTIO_VSOCK_METADATA_FLAGS_REPLY;
> +
> 	trace_virtio_transport_alloc_pkt(src_cid, src_port,
> 					 dst_cid, dst_port,
> 					 len,
> @@ -91,85 +99,26 @@ virtio_transport_alloc_pkt(struct virtio_vsock_pkt_info *info,
> 					 info->op,
> 					 info->flags);
>
> -	return pkt;
> +	return skb;
>
> out:
> -	kfree(pkt->buf);
> -out_pkt:
> -	kfree(pkt);
> +	kfree_skb(skb);
> 	return NULL;
> }
>
> /* Packet capture */
> static struct sk_buff *virtio_transport_build_skb(void *opaque)
> {
> -	struct virtio_vsock_pkt *pkt = opaque;
> -	struct af_vsockmon_hdr *hdr;
> -	struct sk_buff *skb;
> -	size_t payload_len;
> -	void *payload_buf;
> -
> -	/* A packet could be split to fit the RX buffer, so we can retrieve
> -	 * the payload length from the header and the buffer pointer taking
> -	 * care of the offset in the original packet.
> -	 */
> -	payload_len = le32_to_cpu(pkt->hdr.len);
> -	payload_buf = pkt->buf + pkt->off;
> -
> -	skb = alloc_skb(sizeof(*hdr) + sizeof(pkt->hdr) + payload_len,
> -			GFP_ATOMIC);
> -	if (!skb)
> -		return NULL;
> -
> -	hdr = skb_put(skb, sizeof(*hdr));
> -
> -	/* pkt->hdr is little-endian so no need to byteswap here */
> -	hdr->src_cid = pkt->hdr.src_cid;
> -	hdr->src_port = pkt->hdr.src_port;
> -	hdr->dst_cid = pkt->hdr.dst_cid;
> -	hdr->dst_port = pkt->hdr.dst_port;
> -
> -	hdr->transport = cpu_to_le16(AF_VSOCK_TRANSPORT_VIRTIO);
> -	hdr->len = cpu_to_le16(sizeof(pkt->hdr));
> -	memset(hdr->reserved, 0, sizeof(hdr->reserved));
> -
> -	switch (le16_to_cpu(pkt->hdr.op)) {
> -	case VIRTIO_VSOCK_OP_REQUEST:
> -	case VIRTIO_VSOCK_OP_RESPONSE:
> -		hdr->op = cpu_to_le16(AF_VSOCK_OP_CONNECT);
> -		break;
> -	case VIRTIO_VSOCK_OP_RST:
> -	case VIRTIO_VSOCK_OP_SHUTDOWN:
> -		hdr->op = cpu_to_le16(AF_VSOCK_OP_DISCONNECT);
> -		break;
> -	case VIRTIO_VSOCK_OP_RW:
> -		hdr->op = cpu_to_le16(AF_VSOCK_OP_PAYLOAD);
> -		break;
> -	case VIRTIO_VSOCK_OP_CREDIT_UPDATE:
> -	case VIRTIO_VSOCK_OP_CREDIT_REQUEST:
> -		hdr->op = cpu_to_le16(AF_VSOCK_OP_CONTROL);
> -		break;
> -	default:
> -		hdr->op = cpu_to_le16(AF_VSOCK_OP_UNKNOWN);
> -		break;
> -	}
> -
> -	skb_put_data(skb, &pkt->hdr, sizeof(pkt->hdr));
> -
> -	if (payload_len) {
> -		skb_put_data(skb, payload_buf, payload_len);
> -	}
> -
> -	return skb;
> +	return skb_clone((struct sk_buff *)opaque, GFP_ATOMIC);
> }
>
> -void virtio_transport_deliver_tap_pkt(struct virtio_vsock_pkt *pkt)
> +void virtio_transport_deliver_tap_pkt(struct sk_buff *skb)
> {
> -	if (pkt->tap_delivered)
> +	if (vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_TAP_DELIVERED)
> 		return;
>
> -	vsock_deliver_tap(virtio_transport_build_skb, pkt);
> -	pkt->tap_delivered = true;
> +	vsock_deliver_tap(virtio_transport_build_skb, skb);
> +	vsock_metadata(skb)->flags |= VIRTIO_VSOCK_METADATA_FLAGS_TAP_DELIVERED;
> }
> EXPORT_SYMBOL_GPL(virtio_transport_deliver_tap_pkt);
>
> @@ -192,8 +141,9 @@ 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 virtio_vsock_sock *vvs;
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> 	u32 pkt_len = info->pkt_len;
> +	int err;
>
> 	info->type = virtio_transport_get_type(sk_vsock(vsk));
>
> @@ -224,42 +174,47 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
> 		return pkt_len;
>
> -	pkt = virtio_transport_alloc_pkt(info, pkt_len,
> +	skb = virtio_transport_alloc_skb(info, pkt_len,
> 					 src_cid, src_port,
> -					 dst_cid, dst_port);
> -	if (!pkt) {
> +					 dst_cid, dst_port,
> +					 &err);
> +	if (!skb) {
> 		virtio_transport_put_credit(vvs, pkt_len);
> -		return -ENOMEM;
> +		return err;
> 	}
>
> -	virtio_transport_inc_tx_pkt(vvs, pkt);
> +	virtio_transport_inc_tx_pkt(vvs, skb);
> +
> +	err = t_ops->send_pkt(skb);
>
> -	return t_ops->send_pkt(pkt);
> +	return err < 0 ? -ENOMEM : err;
> }
>
> static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
> -					struct virtio_vsock_pkt *pkt)
> +					struct sk_buff *skb)
> {
> -	if (vvs->rx_bytes + pkt->len > vvs->buf_alloc)
> +	if (vvs->rx_bytes + skb->len > vvs->buf_alloc)
> 		return false;
>
> -	vvs->rx_bytes += pkt->len;
> +	vvs->rx_bytes += skb->len;
> 	return true;
> }
>
> static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
> -					struct virtio_vsock_pkt *pkt)
> +					struct sk_buff *skb)
> {
> -	vvs->rx_bytes -= pkt->len;
> -	vvs->fwd_cnt += pkt->len;
> +	vvs->rx_bytes -= skb->len;
> +	vvs->fwd_cnt += skb->len;
> }
>
> -void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
> +void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct sk_buff *skb)
> {
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> +
> 	spin_lock_bh(&vvs->rx_lock);
> 	vvs->last_fwd_cnt = vvs->fwd_cnt;
> -	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
> -	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
> +	hdr->fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
> +	hdr->buf_alloc = cpu_to_le32(vvs->buf_alloc);
> 	spin_unlock_bh(&vvs->rx_lock);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);
> @@ -303,29 +258,29 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
> 				size_t len)
> {
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb, *tmp;
> 	size_t bytes, total = 0, off;
> 	int err = -EFAULT;
>
> 	spin_lock_bh(&vvs->rx_lock);
>
> -	list_for_each_entry(pkt, &vvs->rx_queue, list) {
> -		off = pkt->off;
> +	skb_queue_walk_safe(&vvs->rx_queue, skb,  tmp) {
> +		off = vsock_metadata(skb)->off;
>
> 		if (total == len)
> 			break;
>
> -		while (total < len && off < pkt->len) {
> +		while (total < len && off < skb->len) {
> 			bytes = len - total;
> -			if (bytes > pkt->len - off)
> -				bytes = pkt->len - off;
> +			if (bytes > skb->len - off)
> +				bytes = skb->len - off;
>
> 			/* sk_lock is held by caller so no one else can dequeue.
> 			 * Unlock rx_lock since memcpy_to_msg() may sleep.
> 			 */
> 			spin_unlock_bh(&vvs->rx_lock);
>
> -			err = memcpy_to_msg(msg, pkt->buf + off, bytes);
> +			err = memcpy_to_msg(msg, skb->data + off, bytes);
> 			if (err)
> 				goto out;
>
> @@ -352,37 +307,40 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
> 				   size_t len)
> {
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> 	size_t bytes, total = 0;
> 	u32 free_space;
> 	int err = -EFAULT;
>
> 	spin_lock_bh(&vvs->rx_lock);
> -	while (total < len && !list_empty(&vvs->rx_queue)) {
> -		pkt = list_first_entry(&vvs->rx_queue,
> -				       struct virtio_vsock_pkt, list);
> +	while (total < len && !skb_queue_empty_lockless(&vvs->rx_queue)) {
> +		skb = __skb_dequeue(&vvs->rx_queue);
>
> 		bytes = len - total;
> -		if (bytes > pkt->len - pkt->off)
> -			bytes = pkt->len - pkt->off;
> +		if (bytes > skb->len - vsock_metadata(skb)->off)
> +			bytes = skb->len - vsock_metadata(skb)->off;
>
> 		/* sk_lock is held by caller so no one else can dequeue.
> 		 * Unlock rx_lock since memcpy_to_msg() may sleep.
> 		 */
> 		spin_unlock_bh(&vvs->rx_lock);
>
> -		err = memcpy_to_msg(msg, pkt->buf + pkt->off, bytes);
> +		err = memcpy_to_msg(msg, skb->data + vsock_metadata(skb)->off, bytes);
> 		if (err)
> 			goto out;
>
> 		spin_lock_bh(&vvs->rx_lock);
>
> 		total += bytes;
> -		pkt->off += bytes;
> -		if (pkt->off == pkt->len) {
> -			virtio_transport_dec_rx_pkt(vvs, pkt);
> -			list_del(&pkt->list);
> -			virtio_transport_free_pkt(pkt);
> +		vsock_metadata(skb)->off += bytes;
> +
> +		WARN_ON(vsock_metadata(skb)->off > skb->len);
                ^
Can this ever happen?

> +
> +		if (vsock_metadata(skb)->off == skb->len) {
> +			virtio_transport_dec_rx_pkt(vvs, skb);
> +			consume_skb(skb);
> +		} else {
> +			__skb_queue_head(&vvs->rx_queue, skb);
> 		}
> 	}
>
> @@ -414,7 +372,7 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> 						 int flags)
> {
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> -	struct virtio_vsock_pkt *pkt;
> +	struct sk_buff *skb;
> 	int dequeued_len = 0;
> 	size_t user_buf_len = msg_data_left(msg);
> 	bool msg_ready = false;
> @@ -426,14 +384,24 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> 		return 0;
> 	}
>
> +	if (skb_queue_empty_lockless(&vvs->rx_queue)) {
> +		spin_unlock_bh(&vvs->rx_lock);
> +		return 0;
> +	}
> +
> 	while (!msg_ready) {
> -		pkt = list_first_entry(&vvs->rx_queue, struct virtio_vsock_pkt, list);
> +		struct virtio_vsock_hdr *hdr;
> +
> +		skb = __skb_dequeue(&vvs->rx_queue);
> +		if (!skb)
> +			break;
> +		hdr = vsock_hdr(skb);
>
> 		if (dequeued_len >= 0) {
> 			size_t pkt_len;
> 			size_t bytes_to_copy;
>
> -			pkt_len = (size_t)le32_to_cpu(pkt->hdr.len);
> +			pkt_len = (size_t)le32_to_cpu(hdr->len);
> 			bytes_to_copy = min(user_buf_len, pkt_len);
>
> 			if (bytes_to_copy) {
> @@ -444,7 +412,7 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> 				 */
> 				spin_unlock_bh(&vvs->rx_lock);
>
> -				err = memcpy_to_msg(msg, pkt->buf, bytes_to_copy);
> +				err = memcpy_to_msg(msg, skb->data, bytes_to_copy);
> 				if (err) {
> 					/* Copy of message failed. Rest of
> 					 * fragments will be freed without copy.
> @@ -461,17 +429,16 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
> 				dequeued_len += pkt_len;
> 		}
>
> -		if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM) {
> +		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM) {
> 			msg_ready = true;
> 			vvs->msg_count--;
>
> -			if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOR)
> +			if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOR)
> 				msg->msg_flags |= MSG_EOR;
> 		}
>
> -		virtio_transport_dec_rx_pkt(vvs, pkt);
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> +		virtio_transport_dec_rx_pkt(vvs, skb);
> +		kfree_skb(skb);
> 	}
>
> 	spin_unlock_bh(&vvs->rx_lock);
> @@ -609,7 +576,7 @@ int virtio_transport_do_socket_init(struct vsock_sock *vsk,
>
> 	spin_lock_init(&vvs->rx_lock);
> 	spin_lock_init(&vvs->tx_lock);
> -	INIT_LIST_HEAD(&vvs->rx_queue);
> +	skb_queue_head_init(&vvs->rx_queue);
>
> 	return 0;
> }
> @@ -809,16 +776,16 @@ void virtio_transport_destruct(struct vsock_sock *vsk)
> EXPORT_SYMBOL_GPL(virtio_transport_destruct);
>
> static int virtio_transport_reset(struct vsock_sock *vsk,
> -				  struct virtio_vsock_pkt *pkt)
> +				  struct sk_buff *skb)
> {
> 	struct virtio_vsock_pkt_info info = {
> 		.op = VIRTIO_VSOCK_OP_RST,
> -		.reply = !!pkt,
> +		.reply = !!skb,
> 		.vsk = vsk,
> 	};
>
> 	/* Send RST only if the original pkt is not a RST pkt */
> -	if (pkt && le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_RST)
> +	if (skb && le16_to_cpu(vsock_hdr(skb)->op) == VIRTIO_VSOCK_OP_RST)
> 		return 0;
>
> 	return virtio_transport_send_pkt_info(vsk, &info);
> @@ -828,29 +795,32 @@ static int virtio_transport_reset(struct vsock_sock *vsk,
>  * attempt was made to connect to a socket that does not exist.
>  */
> static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
> -					  struct virtio_vsock_pkt *pkt)
> +					  struct sk_buff *skb)
> {
> -	struct virtio_vsock_pkt *reply;
> +	struct sk_buff *reply;
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	struct virtio_vsock_pkt_info info = {
> 		.op = VIRTIO_VSOCK_OP_RST,
> -		.type = le16_to_cpu(pkt->hdr.type),
> +		.type = le16_to_cpu(hdr->type),
> 		.reply = true,
> 	};
> +	int err;
>
> 	/* Send RST only if the original pkt is not a RST pkt */
> -	if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_RST)
> +	if (le16_to_cpu(hdr->op) == VIRTIO_VSOCK_OP_RST)
> 		return 0;
>
> -	reply = virtio_transport_alloc_pkt(&info, 0,
> -					   le64_to_cpu(pkt->hdr.dst_cid),
> -					   le32_to_cpu(pkt->hdr.dst_port),
> -					   le64_to_cpu(pkt->hdr.src_cid),
> -					   le32_to_cpu(pkt->hdr.src_port));
> +	reply = virtio_transport_alloc_skb(&info, 0,
> +					   le64_to_cpu(hdr->dst_cid),
> +					   le32_to_cpu(hdr->dst_port),
> +					   le64_to_cpu(hdr->src_cid),
> +					   le32_to_cpu(hdr->src_port),
> +					   &err);
> 	if (!reply)
> -		return -ENOMEM;
> +		return err;
>
> 	if (!t) {
> -		virtio_transport_free_pkt(reply);
> +		kfree_skb(reply);
> 		return -ENOTCONN;
> 	}
>
> @@ -861,16 +831,11 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
> static void virtio_transport_remove_sock(struct vsock_sock *vsk)
> {
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> -	struct virtio_vsock_pkt *pkt, *tmp;
>
> 	/* We don't need to take rx_lock, as the socket is closing and we are
> 	 * removing it.
> 	 */
> -	list_for_each_entry_safe(pkt, tmp, &vvs->rx_queue, list) {
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> -
> +	__skb_queue_purge(&vvs->rx_queue);
> 	vsock_remove_sock(vsk);
> }
>
> @@ -984,13 +949,14 @@ EXPORT_SYMBOL_GPL(virtio_transport_release);
>
> static int
> virtio_transport_recv_connecting(struct sock *sk,
> -				 struct virtio_vsock_pkt *pkt)
> +				 struct sk_buff *skb)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	int err;
> 	int skerr;
>
> -	switch (le16_to_cpu(pkt->hdr.op)) {
> +	switch (le16_to_cpu(hdr->op)) {
> 	case VIRTIO_VSOCK_OP_RESPONSE:
> 		sk->sk_state = TCP_ESTABLISHED;
> 		sk->sk_socket->state = SS_CONNECTED;
> @@ -1011,7 +977,7 @@ virtio_transport_recv_connecting(struct sock *sk,
> 	return 0;
>
> destroy:
> -	virtio_transport_reset(vsk, pkt);
> +	virtio_transport_reset(vsk, skb);
> 	sk->sk_state = TCP_CLOSE;
> 	sk->sk_err = skerr;
> 	sk_error_report(sk);
> @@ -1020,34 +986,38 @@ virtio_transport_recv_connecting(struct sock *sk,
>
> static void
> virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> -			      struct virtio_vsock_pkt *pkt)
> +			      struct sk_buff *skb)
> {
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> +	struct virtio_vsock_hdr *hdr;
> 	bool can_enqueue, free_pkt = false;
> +	u32 len;
>
> -	pkt->len = le32_to_cpu(pkt->hdr.len);
> -	pkt->off = 0;
> +	hdr = vsock_hdr(skb);
> +	len = le32_to_cpu(hdr->len);
> +	vsock_metadata(skb)->off = 0;
>
> 	spin_lock_bh(&vvs->rx_lock);
>
> -	can_enqueue = virtio_transport_inc_rx_pkt(vvs, pkt);
> +	can_enqueue = virtio_transport_inc_rx_pkt(vvs, skb);
> 	if (!can_enqueue) {
> 		free_pkt = true;
> 		goto out;
> 	}
>
> -	if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM)
> +	if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM)
> 		vvs->msg_count++;
>
> 	/* Try to copy small packets into the buffer of last packet queued,
> 	 * to avoid wasting memory queueing the entire buffer with a small
> 	 * payload.
> 	 */
> -	if (pkt->len <= GOOD_COPY_LEN && !list_empty(&vvs->rx_queue)) {
> -		struct virtio_vsock_pkt *last_pkt;
> +	if (len <= GOOD_COPY_LEN && !skb_queue_empty_lockless(&vvs->rx_queue)) {
> +		struct virtio_vsock_hdr *last_hdr;
> +		struct sk_buff *last_skb;
>
> -		last_pkt = list_last_entry(&vvs->rx_queue,
> -					   struct virtio_vsock_pkt, list);
> +		last_skb = skb_peek_tail(&vvs->rx_queue);
> +		last_hdr = vsock_hdr(last_skb);
>
> 		/* If there is space in the last packet queued, we copy the
> 		 * new packet in its buffer. We avoid this if the last packet
> @@ -1055,35 +1025,34 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> 		 * delimiter of SEQPACKET message, so 'pkt' is the first packet
> 		 * of a new message.
> 		 */
> -		if ((pkt->len <= last_pkt->buf_len - last_pkt->len) &&
> -		    !(le32_to_cpu(last_pkt->hdr.flags) & VIRTIO_VSOCK_SEQ_EOM)) {
> -			memcpy(last_pkt->buf + last_pkt->len, pkt->buf,
> -			       pkt->len);
> -			last_pkt->len += pkt->len;
> +		if (skb->len < skb_tailroom(last_skb) &&
> +		    !(le32_to_cpu(last_hdr->flags) & VIRTIO_VSOCK_SEQ_EOR)) {
> +			memcpy(skb_put(last_skb, skb->len), skb->data, skb->len);
> 			free_pkt = true;
> -			last_pkt->hdr.flags |= pkt->hdr.flags;
> +			last_hdr->flags |= hdr->flags;
> 			goto out;
> 		}
> 	}
>
> -	list_add_tail(&pkt->list, &vvs->rx_queue);
> +	__skb_queue_tail(&vvs->rx_queue, skb);
>
> out:
> 	spin_unlock_bh(&vvs->rx_lock);
> 	if (free_pkt)
> -		virtio_transport_free_pkt(pkt);
> +		kfree_skb(skb);
> }
>
> static int
> virtio_transport_recv_connected(struct sock *sk,
> -				struct virtio_vsock_pkt *pkt)
> +				struct sk_buff *skb)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	int err = 0;
>
> -	switch (le16_to_cpu(pkt->hdr.op)) {
> +	switch (le16_to_cpu(hdr->op)) {
> 	case VIRTIO_VSOCK_OP_RW:
> -		virtio_transport_recv_enqueue(vsk, pkt);
> +		virtio_transport_recv_enqueue(vsk, skb);
> 		sk->sk_data_ready(sk);
> 		return err;
> 	case VIRTIO_VSOCK_OP_CREDIT_REQUEST:
> @@ -1093,18 +1062,17 @@ virtio_transport_recv_connected(struct sock *sk,
> 		sk->sk_write_space(sk);
> 		break;
> 	case VIRTIO_VSOCK_OP_SHUTDOWN:
> -		if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SHUTDOWN_RCV)
> +		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SHUTDOWN_RCV)
> 			vsk->peer_shutdown |= RCV_SHUTDOWN;
> -		if (le32_to_cpu(pkt->hdr.flags) & VIRTIO_VSOCK_SHUTDOWN_SEND)
> +		if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SHUTDOWN_SEND)
> 			vsk->peer_shutdown |= SEND_SHUTDOWN;
> 		if (vsk->peer_shutdown == SHUTDOWN_MASK &&
> 		    vsock_stream_has_data(vsk) <= 0 &&
> 		    !sock_flag(sk, SOCK_DONE)) {
> 			(void)virtio_transport_reset(vsk, NULL);
> -
> 			virtio_transport_do_close(vsk, true);
> 		}
> -		if (le32_to_cpu(pkt->hdr.flags))
> +		if (le32_to_cpu(vsock_hdr(skb)->flags))
> 			sk->sk_state_change(sk);
> 		break;
> 	case VIRTIO_VSOCK_OP_RST:
> @@ -1115,28 +1083,30 @@ virtio_transport_recv_connected(struct sock *sk,
> 		break;
> 	}
>
> -	virtio_transport_free_pkt(pkt);
> +	kfree_skb(skb);
> 	return err;
> }
>
> static void
> virtio_transport_recv_disconnecting(struct sock *sk,
> -				    struct virtio_vsock_pkt *pkt)
> +				    struct sk_buff *skb)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
>
> -	if (le16_to_cpu(pkt->hdr.op) == VIRTIO_VSOCK_OP_RST)
> +	if (le16_to_cpu(hdr->op) == VIRTIO_VSOCK_OP_RST)
> 		virtio_transport_do_close(vsk, true);
> }
>
> static int
> virtio_transport_send_response(struct vsock_sock *vsk,
> -			       struct virtio_vsock_pkt *pkt)
> +			       struct sk_buff *skb)
> {
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	struct virtio_vsock_pkt_info info = {
> 		.op = VIRTIO_VSOCK_OP_RESPONSE,
> -		.remote_cid = le64_to_cpu(pkt->hdr.src_cid),
> -		.remote_port = le32_to_cpu(pkt->hdr.src_port),
> +		.remote_cid = le64_to_cpu(hdr->src_cid),
> +		.remote_port = le32_to_cpu(hdr->src_port),
> 		.reply = true,
> 		.vsk = vsk,
> 	};
> @@ -1145,10 +1115,11 @@ virtio_transport_send_response(struct vsock_sock *vsk,
> }
>
> static bool virtio_transport_space_update(struct sock *sk,
> -					  struct virtio_vsock_pkt *pkt)
> +					  struct sk_buff *skb)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);
> 	struct virtio_vsock_sock *vvs = vsk->trans;
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	bool space_available;
>
> 	/* Listener sockets are not associated with any transport, so we are
> @@ -1161,8 +1132,8 @@ static bool virtio_transport_space_update(struct sock *sk,
>
> 	/* buf_alloc and fwd_cnt is always included in the hdr */
> 	spin_lock_bh(&vvs->tx_lock);
> -	vvs->peer_buf_alloc = le32_to_cpu(pkt->hdr.buf_alloc);
> -	vvs->peer_fwd_cnt = le32_to_cpu(pkt->hdr.fwd_cnt);
> +	vvs->peer_buf_alloc = le32_to_cpu(hdr->buf_alloc);
> +	vvs->peer_fwd_cnt = le32_to_cpu(hdr->fwd_cnt);
> 	space_available = virtio_transport_has_space(vsk);
> 	spin_unlock_bh(&vvs->tx_lock);
> 	return space_available;
> @@ -1170,27 +1141,28 @@ static bool virtio_transport_space_update(struct sock *sk,
>
> /* Handle server socket */
> static int
> -virtio_transport_recv_listen(struct sock *sk, struct virtio_vsock_pkt *pkt,
> +virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb,
> 			     struct virtio_transport *t)
> {
> 	struct vsock_sock *vsk = vsock_sk(sk);
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
> 	struct vsock_sock *vchild;
> 	struct sock *child;
> 	int ret;
>
> -	if (le16_to_cpu(pkt->hdr.op) != VIRTIO_VSOCK_OP_REQUEST) {
> -		virtio_transport_reset_no_sock(t, pkt);
> +	if (le16_to_cpu(hdr->op) != VIRTIO_VSOCK_OP_REQUEST) {
> +		virtio_transport_reset_no_sock(t, skb);
> 		return -EINVAL;
> 	}
>
> 	if (sk_acceptq_is_full(sk)) {
> -		virtio_transport_reset_no_sock(t, pkt);
> +		virtio_transport_reset_no_sock(t, skb);
> 		return -ENOMEM;
> 	}
>
> 	child = vsock_create_connected(sk);
> 	if (!child) {
> -		virtio_transport_reset_no_sock(t, pkt);
> +		virtio_transport_reset_no_sock(t, skb);
> 		return -ENOMEM;
> 	}
>
> @@ -1201,10 +1173,10 @@ virtio_transport_recv_listen(struct sock *sk, struct virtio_vsock_pkt *pkt,
> 	child->sk_state = TCP_ESTABLISHED;
>
> 	vchild = vsock_sk(child);
> -	vsock_addr_init(&vchild->local_addr, le64_to_cpu(pkt->hdr.dst_cid),
> -			le32_to_cpu(pkt->hdr.dst_port));
> -	vsock_addr_init(&vchild->remote_addr, le64_to_cpu(pkt->hdr.src_cid),
> -			le32_to_cpu(pkt->hdr.src_port));
> +	vsock_addr_init(&vchild->local_addr, le64_to_cpu(hdr->dst_cid),
> +			le32_to_cpu(hdr->dst_port));
> +	vsock_addr_init(&vchild->remote_addr, le64_to_cpu(hdr->src_cid),
> +			le32_to_cpu(hdr->src_port));
>
> 	ret = vsock_assign_transport(vchild, vsk);
> 	/* Transport assigned (looking at remote_addr) must be the same
> @@ -1212,17 +1184,17 @@ virtio_transport_recv_listen(struct sock *sk, struct virtio_vsock_pkt *pkt,
> 	 */
> 	if (ret || vchild->transport != &t->transport) {
> 		release_sock(child);
> -		virtio_transport_reset_no_sock(t, pkt);
> +		virtio_transport_reset_no_sock(t, skb);
> 		sock_put(child);
> 		return ret;
> 	}
>
> -	if (virtio_transport_space_update(child, pkt))
> +	if (virtio_transport_space_update(child, skb))
> 		child->sk_write_space(child);
>
> 	vsock_insert_connected(vchild);
> 	vsock_enqueue_accept(sk, child);
> -	virtio_transport_send_response(vchild, pkt);
> +	virtio_transport_send_response(vchild, skb);
>
> 	release_sock(child);
>
> @@ -1240,29 +1212,30 @@ static bool virtio_transport_valid_type(u16 type)
>  * lock.
>  */
> void virtio_transport_recv_pkt(struct virtio_transport *t,
> -			       struct virtio_vsock_pkt *pkt)
> +			       struct sk_buff *skb)
> {
> 	struct sockaddr_vm src, dst;
> 	struct vsock_sock *vsk;
> 	struct sock *sk;
> 	bool space_available;
> +	struct virtio_vsock_hdr *hdr = vsock_hdr(skb);
>
> -	vsock_addr_init(&src, le64_to_cpu(pkt->hdr.src_cid),
> -			le32_to_cpu(pkt->hdr.src_port));
> -	vsock_addr_init(&dst, le64_to_cpu(pkt->hdr.dst_cid),
> -			le32_to_cpu(pkt->hdr.dst_port));
> +	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));
>
> 	trace_virtio_transport_recv_pkt(src.svm_cid, src.svm_port,
> 					dst.svm_cid, dst.svm_port,
> -					le32_to_cpu(pkt->hdr.len),
> -					le16_to_cpu(pkt->hdr.type),
> -					le16_to_cpu(pkt->hdr.op),
> -					le32_to_cpu(pkt->hdr.flags),
> -					le32_to_cpu(pkt->hdr.buf_alloc),
> -					le32_to_cpu(pkt->hdr.fwd_cnt));
> -
> -	if (!virtio_transport_valid_type(le16_to_cpu(pkt->hdr.type))) {
> -		(void)virtio_transport_reset_no_sock(t, pkt);
> +					le32_to_cpu(hdr->len),
> +					le16_to_cpu(hdr->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))) {
> +		(void)virtio_transport_reset_no_sock(t, skb);
> 		goto free_pkt;
> 	}
>
> @@ -1273,13 +1246,13 @@ 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, pkt);
> +			(void)virtio_transport_reset_no_sock(t, skb);
> 			goto free_pkt;
> 		}
> 	}
>
> -	if (virtio_transport_get_type(sk) != le16_to_cpu(pkt->hdr.type)) {
> -		(void)virtio_transport_reset_no_sock(t, pkt);
> +	if (virtio_transport_get_type(sk) != le16_to_cpu(hdr->type)) {
> +		(void)virtio_transport_reset_no_sock(t, skb);
> 		sock_put(sk);
> 		goto free_pkt;
> 	}
> @@ -1290,13 +1263,13 @@ 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, pkt);
> +		(void)virtio_transport_reset_no_sock(t, skb);
> 		release_sock(sk);
> 		sock_put(sk);
> 		goto free_pkt;
> 	}
>
> -	space_available = virtio_transport_space_update(sk, pkt);
> +	space_available = virtio_transport_space_update(sk, skb);
>
> 	/* Update CID in case it has changed after a transport reset event */
> 	if (vsk->local_addr.svm_cid != VMADDR_CID_ANY)
> @@ -1307,23 +1280,23 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
>
> 	switch (sk->sk_state) {
> 	case TCP_LISTEN:
> -		virtio_transport_recv_listen(sk, pkt, t);
> -		virtio_transport_free_pkt(pkt);
> +		virtio_transport_recv_listen(sk, skb, t);
> +		kfree_skb(skb);
> 		break;
> 	case TCP_SYN_SENT:
> -		virtio_transport_recv_connecting(sk, pkt);
> -		virtio_transport_free_pkt(pkt);
> +		virtio_transport_recv_connecting(sk, skb);
> +		kfree_skb(skb);
> 		break;
> 	case TCP_ESTABLISHED:
> -		virtio_transport_recv_connected(sk, pkt);
> +		virtio_transport_recv_connected(sk, skb);
> 		break;
> 	case TCP_CLOSING:
> -		virtio_transport_recv_disconnecting(sk, pkt);
> -		virtio_transport_free_pkt(pkt);
> +		virtio_transport_recv_disconnecting(sk, skb);
> +		kfree_skb(skb);
> 		break;
> 	default:
> -		(void)virtio_transport_reset_no_sock(t, pkt);
> -		virtio_transport_free_pkt(pkt);
> +		(void)virtio_transport_reset_no_sock(t, skb);
> +		kfree_skb(skb);
> 		break;
> 	}
>
> @@ -1336,16 +1309,42 @@ void virtio_transport_recv_pkt(struct virtio_transport *t,
> 	return;
>
> free_pkt:
> -	virtio_transport_free_pkt(pkt);
> +	kfree(skb);
> }
> EXPORT_SYMBOL_GPL(virtio_transport_recv_pkt);
>
> -void virtio_transport_free_pkt(struct virtio_vsock_pkt *pkt)
> +/* Remove skbs found in a queue that have a vsk that matches.
> + *
> + * Each skb is freed.
> + *
> + * Returns the count of skbs that were reply packets.
> + */
> +int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *queue)
> {
> -	kfree(pkt->buf);
> -	kfree(pkt);
> +	int cnt = 0;
> +	struct sk_buff *skb, *tmp;
> +	struct sk_buff_head freeme;
> +
> +	skb_queue_head_init(&freeme);
> +
> +	spin_lock_bh(&queue->lock);
> +	skb_queue_walk_safe(queue, skb, tmp) {
> +		if (vsock_sk(skb->sk) != vsk)
> +			continue;
> +
> +		__skb_unlink(skb, queue);
> +		skb_queue_tail(&freeme, skb);
> +
> +		if (vsock_metadata(skb)->flags & VIRTIO_VSOCK_METADATA_FLAGS_REPLY)
> +			cnt++;
> +	}
> +	spin_unlock_bh(&queue->lock);
> +
> +	skb_queue_purge(&freeme);
> +
> +	return cnt;
> }
> -EXPORT_SYMBOL_GPL(virtio_transport_free_pkt);
> +EXPORT_SYMBOL_GPL(virtio_transport_purge_skbs);
>
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Asias He");
> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
> index 169a8cf65b39..792128e66869 100644
> --- a/net/vmw_vsock/vsock_loopback.c
> +++ b/net/vmw_vsock/vsock_loopback.c
> @@ -16,7 +16,7 @@ struct vsock_loopback {
> 	struct workqueue_struct *workqueue;
>
> 	spinlock_t pkt_list_lock; /* protects pkt_list */
> -	struct list_head pkt_list;
> +	struct sk_buff_head pkt_queue;
> 	struct work_struct pkt_work;
> };
>
> @@ -27,13 +27,13 @@ static u32 vsock_loopback_get_local_cid(void)
> 	return VMADDR_CID_LOCAL;
> }
>
> -static int vsock_loopback_send_pkt(struct virtio_vsock_pkt *pkt)
> +static int vsock_loopback_send_pkt(struct sk_buff *skb)
> {
> 	struct vsock_loopback *vsock = &the_vsock_loopback;
> -	int len = pkt->len;
> +	int len = skb->len;
>
> 	spin_lock_bh(&vsock->pkt_list_lock);
> -	list_add_tail(&pkt->list, &vsock->pkt_list);
> +	skb_queue_tail(&vsock->pkt_queue, skb);
> 	spin_unlock_bh(&vsock->pkt_list_lock);
>
> 	queue_work(vsock->workqueue, &vsock->pkt_work);
> @@ -44,21 +44,8 @@ static int vsock_loopback_send_pkt(struct virtio_vsock_pkt *pkt)
> static int vsock_loopback_cancel_pkt(struct vsock_sock *vsk)
> {
> 	struct vsock_loopback *vsock = &the_vsock_loopback;
> -	struct virtio_vsock_pkt *pkt, *n;
> -	LIST_HEAD(freeme);
>
> -	spin_lock_bh(&vsock->pkt_list_lock);
> -	list_for_each_entry_safe(pkt, n, &vsock->pkt_list, list) {
> -		if (pkt->vsk != vsk)
> -			continue;
> -		list_move(&pkt->list, &freeme);
> -	}
> -	spin_unlock_bh(&vsock->pkt_list_lock);
> -
> -	list_for_each_entry_safe(pkt, n, &freeme, list) {
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> +	virtio_transport_purge_skbs(vsk, &vsock->pkt_queue);
>
> 	return 0;
> }
> @@ -121,20 +108,18 @@ static void vsock_loopback_work(struct work_struct *work)
> {
> 	struct vsock_loopback *vsock =
> 		container_of(work, struct vsock_loopback, pkt_work);
> -	LIST_HEAD(pkts);
> +	struct sk_buff_head pkts;
> +	struct sk_buff *skb;
> +
> +	skb_queue_head_init(&pkts);
>
> 	spin_lock_bh(&vsock->pkt_list_lock);
> -	list_splice_init(&vsock->pkt_list, &pkts);
> +	skb_queue_splice_init(&vsock->pkt_queue, &pkts);
> 	spin_unlock_bh(&vsock->pkt_list_lock);
>
> -	while (!list_empty(&pkts)) {
> -		struct virtio_vsock_pkt *pkt;
> -
> -		pkt = list_first_entry(&pkts, struct virtio_vsock_pkt, list);
> -		list_del_init(&pkt->list);
> -
> -		virtio_transport_deliver_tap_pkt(pkt);
> -		virtio_transport_recv_pkt(&loopback_transport, pkt);
> +	while ((skb = skb_dequeue(&pkts))) {
> +		virtio_transport_deliver_tap_pkt(skb);
> +		virtio_transport_recv_pkt(&loopback_transport, skb);
> 	}
> }
>
> @@ -148,7 +133,7 @@ static int __init vsock_loopback_init(void)
> 		return -ENOMEM;
>
> 	spin_lock_init(&vsock->pkt_list_lock);
> -	INIT_LIST_HEAD(&vsock->pkt_list);
> +	skb_queue_head_init(&vsock->pkt_queue);
> 	INIT_WORK(&vsock->pkt_work, vsock_loopback_work);
>
> 	ret = vsock_core_register(&loopback_transport.transport,
> @@ -166,19 +151,13 @@ static int __init vsock_loopback_init(void)
> static void __exit vsock_loopback_exit(void)
> {
> 	struct vsock_loopback *vsock = &the_vsock_loopback;
> -	struct virtio_vsock_pkt *pkt;
>
> 	vsock_core_unregister(&loopback_transport.transport);
>
> 	flush_work(&vsock->pkt_work);
>
> 	spin_lock_bh(&vsock->pkt_list_lock);
> -	while (!list_empty(&vsock->pkt_list)) {
> -		pkt = list_first_entry(&vsock->pkt_list,
> -				       struct virtio_vsock_pkt, list);
> -		list_del(&pkt->list);
> -		virtio_transport_free_pkt(pkt);
> -	}
> +	skb_queue_purge(&vsock->pkt_queue);
> 	spin_unlock_bh(&vsock->pkt_list_lock);
>
> 	destroy_workqueue(vsock->workqueue);
> --
> 2.35.1

Not for this patch, but if we implement this change, it would be nice to 
have APIs that all transports can re-use. (Like we do in vsock_loopback 
which has nothing to do with virtio, but we had reused virtio_vsock_pkt 
for convenience)

Good job so far!

Thanks,
Stefano