Date:   Thu, 15 Dec 2022 04:04:53 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     Bobby Eshleman <bobby.eshleman@...edance.com>,
        Bobby Eshleman <bobbyeshleman@...il.com>,
        Cong Wang <cong.wang@...edance.com>,
        Jiang Wang <jiang.wang@...edance.com>,
        Krasnov Arseniy <oxffffaa@...il.com>,
        Stefan Hajnoczi <stefanha@...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>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v8] virtio/vsock: replace virtio_vsock_pkt with
 sk_buff

On Thu, Dec 15, 2022 at 09:47:57AM +0100, Stefano Garzarella wrote:
> On Thu, Dec 15, 2022 at 04:36:44AM +0000, Bobby Eshleman wrote:
> > This commit changes virtio/vsock to use sk_buff instead of
> > virtio_vsock_pkt. Beyond better conforming to other net code, using
> > sk_buff allows vsock to use sk_buff-dependent features in the future
> > (such as sockmap) and improves throughput.
> > 
> > This patch introduces the following performance changes:
> > 
> > Tool/Config: uperf w/ 64 threads, SOCK_STREAM
> > Test Runs: 5, mean of results
> > Before: commit 95ec6bce2a0b ("Merge branch 'net-ipa-more-endpoints'")
> > 
> > Test: 64KB, g2h
> > Before: 21.63 Gb/s
> > After: 25.59 Gb/s (+18%)
> > 
> > Test: 16B, g2h
> > Before: 11.86 Mb/s
> > After: 17.41 Mb/s (+46%)
> > 
> > Test: 64KB, h2g
> > Before: 2.15 Gb/s
> > After: 3.6 Gb/s (+67%)
> > 
> > Test: 16B, h2g
> > Before: 14.38 Mb/s
> > After: 18.43 Mb/s (+28%)
> > 
> > Signed-off-by: Bobby Eshleman <bobby.eshleman@...edance.com>
> > ---
> > 
> > Testing: passed vsock_test h2g and g2h
> > Note2: net-next is closed, but sending out now in case more comments
> > roll in, as discussed here:
> > https://lore.kernel.org/all/Y34SoH1nFTXXLWbK@bullseye/
> > 
> > Changes in v8:
> > - vhost/vsock: remove unused enum
> > - vhost/vsock: use spin_lock_bh() instead of spin_lock()
> > - vsock/loopback: use __skb_dequeue instead of skb_dequeue
> > 
> > Changes in v7:
> > - use skb_queue_empty() instead of skb_queue_empty_lockless()
> > 
> > Changes in v6:
> > - use skb->cb instead of skb->_skb_refdst
> > - use lock-free __skb_queue_purge for rx_queue when rx_lock held
> > 
> > Changes in v5:
> > - last_skb instead of skb: last_hdr->len = cpu_to_le32(last_skb->len)
> > 
> > Changes in v4:
> > - vdso/bits.h -> linux/bits.h
> > - add virtio_vsock_alloc_skb() helper
> > - virtio/vsock: rename buf_len -> total_len
> > - update last_hdr->len
> > - fix build_skb() for vsockmon (tested)
> > - add queue helpers
> > - use spin_{unlock/lock}_bh() instead of spin_lock()/spin_unlock()
> > - note: I only ran a few g2h tests to check that this change
> >  had no perf impact. The above data is still from patch
> >  v3.
> > 
> > Changes in v3:
> > - fix seqpacket bug
> > - use zero in vhost_add_used(..., 0) device doesn't write to buffer
> > - use xmas tree style declarations
> > - vsock_hdr() -> virtio_vsock_hdr() and other include file style fixes
> > - no skb merging
> > - save space by not using vsock_metadata
> > - use _skb_refdst instead of skb buffer space for flags
> > - use skb_pull() to keep track of read bytes instead of using an an
> >  extra variable 'off' in the skb buffer space
> > - remove unnecessary sk_allocation assignment
> > - do not zero hdr needlessly
> > - introduce virtio_transport_skb_len() because skb->len changes now
> > - use spin_lock() directly on queue lock instead of sk_buff_head helpers
> >  which use spin_lock_irqsave() (e.g., skb_dequeue)
> > - do not reduce buffer size to be page size divisible
> > - Note: the biggest performance change came from loosening the spinlock
> >  variation and not reducing the buffer size.
> > 
> > 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                   | 213 +++++-------
> > include/linux/virtio_vsock.h            | 126 +++++--
> > net/vmw_vsock/virtio_transport.c        | 149 +++------
> > net/vmw_vsock/virtio_transport_common.c | 422 +++++++++++++-----------
> > net/vmw_vsock/vsock_loopback.c          |  51 +--
> > 5 files changed, 495 insertions(+), 466 deletions(-)
> > 
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index 5703775af129..ee0a00432cb1 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;
> > 
> > @@ -108,40 +107,33 @@ vhost_transport_do_send_pkt(struct vhost_vsock
> > *vsock,
> > 	vhost_disable_notify(&vsock->dev, vq);
> > 
> > 	do {
> > -		struct virtio_vsock_pkt *pkt;
> > +		struct virtio_vsock_hdr *hdr;
> > +		size_t iov_len, payload_len;
> > 		struct iov_iter iov_iter;
> > +		u32 flags_to_restore = 0;
> > +		struct sk_buff *skb;
> > 		unsigned out, in;
> > 		size_t nbytes;
> > -		size_t iov_len, payload_len;
> > 		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);
> > +		spin_lock_bh(&vsock->send_pkt_queue.lock);
> > +		skb = __skb_dequeue(&vsock->send_pkt_queue);
> > +		spin_unlock_bh(&vsock->send_pkt_queue.lock);
> 
> Sorry for coming late, but I just commented in Paolo's reply.
> Here I think we can directly use the new virtio_vsock_skb_dequeue().

Yea, pretty late.
And using that will prevent me from merging this since it's not in my tree yet.
We can do a cleanup patch on top.

> With that fixed, you can put my R-b:
> 
> Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>
> 
> Below I left a little comment.
> 
> > +
> > +		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);
> > +			virtio_vsock_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);
> > -
> > +			virtio_vsock_skb_queue_head(&vsock->send_pkt_queue, skb);
> > 			/* We cannot finish yet if more buffers snuck in while
> > 			 * re-enabling notify.
> > 			 */
> > @@ -153,26 +145,27 @@ 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;
> > +		hdr = virtio_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 +178,30 @@ 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,
> > -				      &iov_iter);
> > +		nbytes = copy_to_iter(skb->data, 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;
> > +		skb_pull(skb, 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 (skb->len > 0) {
> > +			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);
> > +			virtio_vsock_skb_clear_tap_delivered(skb);
> > +			virtio_vsock_skb_queue_head(&vsock->send_pkt_queue, skb);
> > 		} else {
> > -			if (pkt->reply) {
> > +			if (virtio_vsock_skb_reply(skb)) {
> > 				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 virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
> > 	struct vhost_vsock *vsock;
> > -	int len = pkt->len;
> > +	int len = skb->len;
> > 
> > 	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 (virtio_vsock_skb_reply(skb))
> > 		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_vsock_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];
> > @@ -352,12 +324,14 @@ 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 virtio_vsock_hdr *hdr;
> > 	struct iov_iter iov_iter;
> > +	struct sk_buff *skb;
> > +	size_t payload_len;
> > 	size_t nbytes;
> > 	size_t len;
> > 
> > @@ -366,50 +340,47 @@ 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 */
> > +	skb = virtio_vsock_alloc_skb(len, GFP_KERNEL);
> > +	if (!skb)
> > 		return NULL;
> > 
> > -	len = iov_length(vq->iov, out);
> > 	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 = virtio_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);
> > +	payload_len = le32_to_cpu(hdr->len);
> > 
> > 	/* No payload */
> > -	if (!pkt->len)
> > -		return pkt;
> > +	if (!payload_len)
> > +		return skb;
> > 
> > 	/* The pkt is too big */
> > -	if (pkt->len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> > -		kfree(pkt);
> > +	if (payload_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE) {
> > +		kfree_skb(skb);
> > 		return NULL;
> > 	}
> > 
> > -	pkt->buf = kvmalloc(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, payload_len, &iov_iter);
> > +	if (nbytes != payload_len) {
> > +		vq_err(vq, "Expected %zu byte payload, got %zu bytes\n",
> > +		       payload_len, nbytes);
> > +		kfree_skb(skb);
> > 		return NULL;
> > 	}
> > 
> > -	return pkt;
> > +	return skb;
> > }
> > 
> > /* Is there space left for replies to rx packets? */
> > @@ -496,9 +467,9 @@ 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;
> > 	int head, pkts = 0, total_len = 0;
> > 	unsigned int out, in;
> > +	struct sk_buff *skb;
> > 	bool added = false;
> > 
> > 	mutex_lock(&vq->mutex);
> > @@ -511,6 +482,8 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
> > 
> > 	vhost_disable_notify(&vsock->dev, vq);
> > 	do {
> > +		struct virtio_vsock_hdr *hdr;
> > +
> > 		if (!vhost_vsock_more_replies(vsock)) {
> > 			/* Stop tx until the device processes already
> > 			 * pending replies.  Leave tx virtqueue
> > @@ -532,24 +505,26 @@ static void vhost_vsock_handle_tx_kick(struct vhost_work *work)
> > 			break;
> > 		}
> > 
> > -		pkt = vhost_vsock_alloc_pkt(vq, out, in);
> > -		if (!pkt) {
> > +		skb = vhost_vsock_alloc_skb(vq, out, in);
> > +		if (!skb) {
> > 			vq_err(vq, "Faulted on pkt\n");
> > 			continue;
> > 		}
> > 
> > -		total_len += sizeof(pkt->hdr) + pkt->len;
> > +		total_len += sizeof(*hdr) + skb->len;
> > 
> > 		/* Deliver to monitoring devices all received packets */
> > -		virtio_transport_deliver_tap_pkt(pkt);
> > +		virtio_transport_deliver_tap_pkt(skb);
> > +
> > +		hdr = virtio_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);
> > 		added = true;
> > @@ -693,8 +668,7 @@ 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 +734,7 @@ 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);
> > +	virtio_vsock_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..7ed943615271 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -7,6 +7,106 @@
> > #include <net/sock.h>
> > #include <net/af_vsock.h>
> > 
> > +#define VIRTIO_VSOCK_SKB_HEADROOM (sizeof(struct virtio_vsock_hdr))
> > +
> > +struct virtio_vsock_skb_cb {
> > +	bool reply;
> > +	bool tap_delivered;
> > +};
> > +
> > +#define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb))
> > +
> > +static inline struct virtio_vsock_hdr *virtio_vsock_hdr(struct sk_buff *skb)
> > +{
> > +	return (struct virtio_vsock_hdr *)skb->head;
> > +}
> > +
> > +static inline bool virtio_vsock_skb_reply(struct sk_buff *skb)
> > +{
> > +	return VIRTIO_VSOCK_SKB_CB(skb)->reply;
> > +}
> > +
> > +static inline void virtio_vsock_skb_set_reply(struct sk_buff *skb)
> > +{
> > +	VIRTIO_VSOCK_SKB_CB(skb)->reply = true;
> > +}
> > +
> > +static inline bool virtio_vsock_skb_tap_delivered(struct sk_buff *skb)
> > +{
> > +	return VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered;
> > +}
> > +
> > +static inline void virtio_vsock_skb_set_tap_delivered(struct sk_buff *skb)
> > +{
> > +	VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered = true;
> > +}
> > +
> > +static inline void virtio_vsock_skb_clear_tap_delivered(struct sk_buff *skb)
> > +{
> > +	VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered = false;
> > +}
> 
> Maybe, we can have a single
> 
> virtio_vsock_skb_set_tap_delivered(struct sk_buff *skb,
>                                    bool tap_delivered)
> 
> to be used in both cases.
> 
> Anyway, I don't have a strong opinion on that.
> 
> Thanks,
> Stefano

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