Merge branch 'vsock-virtio-vhost-msg_zerocopy-preparations'

Arseniy Krasnov says:

====================
vsock/virtio/vhost: MSG_ZEROCOPY preparations

this patchset is first of three parts of another big patchset for
MSG_ZEROCOPY flag support:
https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@sberdevices.ru/

During review of this series, Stefano Garzarella <sgarzare@redhat.com>
suggested to split it for three parts to simplify review and merging:

1) virtio and vhost updates (for fragged skbs) <--- this patchset
2) AF_VSOCK updates (allows to enable MSG_ZEROCOPY mode and read
   tx completions) and update for Documentation/.
3) Updates for tests and utils.

This series enables handling of fragged skbs in virtio and vhost parts.
Newly logic won't be triggered, because SO_ZEROCOPY options is still
impossible to enable at this moment (next bunch of patches from big
set above will enable it).
====================

Link: https://lore.kernel.org/r/20230916130918.4105122-1-avkrasnov@salutedevices.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

5 files changed, 348 insertions, 87 deletions

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 817d377a3f36..83711aad855c 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -114,6 +114,7 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		struct sk_buff *skb;
 		unsigned out, in;
 		size_t nbytes;
+		u32 offset;
 		int head;
 
 		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
@@ -156,7 +157,8 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		}
 
 		iov_iter_init(&iov_iter, ITER_DEST, &vq->iov[out], in, iov_len);
-		payload_len = skb->len;
+		offset = VIRTIO_VSOCK_SKB_CB(skb)->offset;
+		payload_len = skb->len - offset;
 		hdr = virtio_vsock_hdr(skb);
 
 		/* If the packet is greater than the space available in the
@@ -197,8 +199,10 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 			break;
 		}
 
-		nbytes = copy_to_iter(skb->data, payload_len, &iov_iter);
-		if (nbytes != payload_len) {
+		if (skb_copy_datagram_iter(skb,
+					   offset,
+					   &iov_iter,
+					   payload_len)) {
 			kfree_skb(skb);
 			vq_err(vq, "Faulted on copying pkt buf\n");
 			break;
@@ -212,13 +216,13 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		vhost_add_used(vq, head, sizeof(*hdr) + payload_len);
 		added = true;
 
-		skb_pull(skb, payload_len);
+		VIRTIO_VSOCK_SKB_CB(skb)->offset += 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 (skb->len > 0) {
+		if (VIRTIO_VSOCK_SKB_CB(skb)->offset < skb->len) {
 			hdr->flags |= cpu_to_le32(flags_to_restore);
 
 			/* We are queueing the same skb to handle
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index c58453699ee9..ebb3ce63d64d 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -12,6 +12,7 @@
 struct virtio_vsock_skb_cb {
 	bool reply;
 	bool tap_delivered;
+	u32 offset;
 };
 
 #define VIRTIO_VSOCK_SKB_CB(skb) ((struct virtio_vsock_skb_cb *)((skb)->cb))
@@ -159,6 +160,15 @@ struct virtio_transport {
 
 	/* Takes ownership of the packet */
 	int (*send_pkt)(struct sk_buff *skb);
+
+	/* Used in MSG_ZEROCOPY mode. Checks, that provided data
+	 * (number of buffers) could be transmitted with zerocopy
+	 * mode. If this callback is not implemented for the current
+	 * transport - this means that this transport doesn't need
+	 * extra checks and can perform zerocopy transmission by
+	 * default.
+	 */
+	bool (*can_msgzerocopy)(int bufs_num);
 };
 
 ssize_t
diff --git a/include/trace/events/vsock_virtio_transport_common.h b/include/trace/events/vsock_virtio_transport_common.h
index d0b3f0ea9ba1..f1ebe36787c3 100644
--- a/include/trace/events/vsock_virtio_transport_common.h
+++ b/include/trace/events/vsock_virtio_transport_common.h
@@ -43,7 +43,8 @@ TRACE_EVENT(virtio_transport_alloc_pkt,
 		 __u32 len,
 		 __u16 type,
 		 __u16 op,
-		 __u32 flags
+		 __u32 flags,
+		 bool zcopy
 	),
 	TP_ARGS(
 		src_cid, src_port,
@@ -51,7 +52,8 @@ TRACE_EVENT(virtio_transport_alloc_pkt,
 		len,
 		type,
 		op,
-		flags
+		flags,
+		zcopy
 	),
 	TP_STRUCT__entry(
 		__field(__u32, src_cid)
@@ -62,6 +64,7 @@ TRACE_EVENT(virtio_transport_alloc_pkt,
 		__field(__u16, type)
 		__field(__u16, op)
 		__field(__u32, flags)
+		__field(bool, zcopy)
 	),
 	TP_fast_assign(
 		__entry->src_cid = src_cid;
@@ -72,14 +75,15 @@ TRACE_EVENT(virtio_transport_alloc_pkt,
 		__entry->type = type;
 		__entry->op = op;
 		__entry->flags = flags;
+		__entry->zcopy = zcopy;
 	),
-	TP_printk("%u:%u -> %u:%u len=%u type=%s op=%s flags=%#x",
+	TP_printk("%u:%u -> %u:%u len=%u type=%s op=%s flags=%#x zcopy=%s",
 		  __entry->src_cid, __entry->src_port,
 		  __entry->dst_cid, __entry->dst_port,
 		  __entry->len,
 		  show_type(__entry->type),
 		  show_op(__entry->op),
-		  __entry->flags)
+		  __entry->flags, __entry->zcopy ? "true" : "false")
 );
 
 TRACE_EVENT(virtio_transport_recv_pkt,
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index e95df847176b..09ba3128e759 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -63,6 +63,17 @@ struct virtio_vsock {
 
 	u32 guest_cid;
 	bool seqpacket_allow;
+
+	/* These fields are used only in tx path in function
+	 * 'virtio_transport_send_pkt_work()', so to save
+	 * stack space in it, place both of them here. Each
+	 * pointer from 'out_sgs' points to the corresponding
+	 * element in 'out_bufs' - this is initialized in
+	 * 'virtio_vsock_probe()'. Both fields are protected
+	 * by 'tx_lock'. +1 is needed for packet header.
+	 */
+	struct scatterlist *out_sgs[MAX_SKB_FRAGS + 1];
+	struct scatterlist out_bufs[MAX_SKB_FRAGS + 1];
 };
 
 static u32 virtio_transport_get_local_cid(void)
@@ -100,8 +111,8 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 	vq = vsock->vqs[VSOCK_VQ_TX];
 
 	for (;;) {
-		struct scatterlist hdr, buf, *sgs[2];
 		int ret, in_sg = 0, out_sg = 0;
+		struct scatterlist **sgs;
 		struct sk_buff *skb;
 		bool reply;
 
@@ -111,12 +122,43 @@ virtio_transport_send_pkt_work(struct work_struct *work)
 
 		virtio_transport_deliver_tap_pkt(skb);
 		reply = virtio_vsock_skb_reply(skb);
-
-		sg_init_one(&hdr, virtio_vsock_hdr(skb), sizeof(*virtio_vsock_hdr(skb)));
-		sgs[out_sg++] = &hdr;
-		if (skb->len > 0) {
-			sg_init_one(&buf, skb->data, skb->len);
-			sgs[out_sg++] = &buf;
+		sgs = vsock->out_sgs;
+		sg_init_one(sgs[out_sg], virtio_vsock_hdr(skb),
+			    sizeof(*virtio_vsock_hdr(skb)));
+		out_sg++;
+
+		if (!skb_is_nonlinear(skb)) {
+			if (skb->len > 0) {
+				sg_init_one(sgs[out_sg], skb->data, skb->len);
+				out_sg++;
+			}
+		} else {
+			struct skb_shared_info *si;
+			int i;
+
+			/* If skb is nonlinear, then its buffer must contain
+			 * only header and nothing more. Data is stored in
+			 * the fragged part.
+			 */
+			WARN_ON_ONCE(skb_headroom(skb) != sizeof(*virtio_vsock_hdr(skb)));
+
+			si = skb_shinfo(skb);
+
+			for (i = 0; i < si->nr_frags; i++) {
+				skb_frag_t *skb_frag = &si->frags[i];
+				void *va;
+
+				/* We will use 'page_to_virt()' for the userspace page
+				 * here, because virtio or dma-mapping layers will call
+				 * 'virt_to_phys()' later to fill the buffer descriptor.
+				 * We don't touch memory at "virtual" address of this page.
+				 */
+				va = page_to_virt(skb_frag->bv_page);
+				sg_init_one(sgs[out_sg],
+					    va + skb_frag->bv_offset,
+					    skb_frag->bv_len);
+				out_sg++;
+			}
 		}
 
 		ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
@@ -413,6 +455,37 @@ static void virtio_vsock_rx_done(struct virtqueue *vq)
 	queue_work(virtio_vsock_workqueue, &vsock->rx_work);
 }
 
+static bool virtio_transport_can_msgzerocopy(int bufs_num)
+{
+	struct virtio_vsock *vsock;
+	bool res = false;
+
+	rcu_read_lock();
+
+	vsock = rcu_dereference(the_virtio_vsock);
+	if (vsock) {
+		struct virtqueue *vq = vsock->vqs[VSOCK_VQ_TX];
+
+		/* Check that tx queue is large enough to keep whole
+		 * data to send. This is needed, because when there is
+		 * not enough free space in the queue, current skb to
+		 * send will be reinserted to the head of tx list of
+		 * the socket to retry transmission later, so if skb
+		 * is bigger than whole queue, it will be reinserted
+		 * again and again, thus blocking other skbs to be sent.
+		 * Each page of the user provided buffer will be added
+		 * as a single buffer to the tx virtqueue, so compare
+		 * number of pages against maximum capacity of the queue.
+		 */
+		if (bufs_num <= vq->num_max)
+			res = true;
+	}
+
+	rcu_read_unlock();
+
+	return res;
+}
+
 static bool virtio_transport_seqpacket_allow(u32 remote_cid);
 
 static struct virtio_transport virtio_transport = {
@@ -462,6 +535,7 @@ static struct virtio_transport virtio_transport = {
 	},
 
 	.send_pkt = virtio_transport_send_pkt,
+	.can_msgzerocopy = virtio_transport_can_msgzerocopy,
 };
 
 static bool virtio_transport_seqpacket_allow(u32 remote_cid)
@@ -621,6 +695,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
 {
 	struct virtio_vsock *vsock = NULL;
 	int ret;
+	int i;
 
 	ret = mutex_lock_interruptible(&the_virtio_vsock_mutex);
 	if (ret)
@@ -663,6 +738,9 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
 	if (ret < 0)
 		goto out;
 
+	for (i = 0; i < ARRAY_SIZE(vsock->out_sgs); i++)
+		vsock->out_sgs[i] = &vsock->out_bufs[i];
+
 	rcu_assign_pointer(the_virtio_vsock, vsock);
 
 	mutex_unlock(&the_virtio_vsock_mutex);
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 352d042b130b..e22c81435ef7 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -37,27 +37,89 @@ virtio_transport_get_ops(struct vsock_sock *vsk)
 	return container_of(t, struct virtio_transport, transport);
 }
 
-/* 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)
-{
-	const size_t skb_len = VIRTIO_VSOCK_SKB_HEADROOM + len;
-	struct virtio_vsock_hdr *hdr;
-	struct sk_buff *skb;
-	void *payload;
-	int err;
+static bool virtio_transport_can_zcopy(const struct virtio_transport *t_ops,
+				       struct virtio_vsock_pkt_info *info,
+				       size_t pkt_len)
+{
+	struct iov_iter *iov_iter;
 
-	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
-	if (!skb)
-		return NULL;
+	if (!info->msg)
+		return false;
+
+	iov_iter = &info->msg->msg_iter;
+
+	if (iov_iter->iov_offset)
+		return false;
+
+	/* We can't send whole iov. */
+	if (iov_iter->count > pkt_len)
+		return false;
+
+	/* Check that transport can send data in zerocopy mode. */
+	t_ops = virtio_transport_get_ops(info->vsk);
+
+	if (t_ops->can_msgzerocopy) {
+		int pages_in_iov = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
+		int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);
+
+		/* +1 is for packet header. */
+		return t_ops->can_msgzerocopy(pages_to_send + 1);
+	}
+
+	return true;
+}
+
+static int virtio_transport_init_zcopy_skb(struct vsock_sock *vsk,
+					   struct sk_buff *skb,
+					   struct msghdr *msg,
+					   bool zerocopy)
+{
+	struct ubuf_info *uarg;
+
+	if (msg->msg_ubuf) {
+		uarg = msg->msg_ubuf;
+		net_zcopy_get(uarg);
+	} else {
+		struct iov_iter *iter = &msg->msg_iter;
+		struct ubuf_info_msgzc *uarg_zc;
+
+		uarg = msg_zerocopy_realloc(sk_vsock(vsk),
+					    iter->count,
+					    NULL);
+		if (!uarg)
+			return -1;
+
+		uarg_zc = uarg_to_msgzc(uarg);
+		uarg_zc->zerocopy = zerocopy ? 1 : 0;
+	}
+
+	skb_zcopy_init(skb, uarg);
+
+	return 0;
+}
+
+static int virtio_transport_fill_skb(struct sk_buff *skb,
+				     struct virtio_vsock_pkt_info *info,
+				     size_t len,
+				     bool zcopy)
+{
+	if (zcopy)
+		return __zerocopy_sg_from_iter(info->msg, NULL, skb,
+					       &info->msg->msg_iter,
+					       len);
+
+	return memcpy_from_msg(skb_put(skb, len), info->msg, len);
+}
+
+static void virtio_transport_init_hdr(struct sk_buff *skb,
+				      struct virtio_vsock_pkt_info *info,
+				      size_t payload_len,
+				      u32 src_cid,
+				      u32 src_port,
+				      u32 dst_cid,
+				      u32 dst_port)
+{
+	struct virtio_vsock_hdr *hdr;
 
 	hdr = virtio_vsock_hdr(skb);
 	hdr->type	= cpu_to_le16(info->type);
@@ -67,43 +129,28 @@ virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
 	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);
-
-	if (info->msg && len > 0) {
-		payload = skb_put(skb, len);
-		err = memcpy_from_msg(payload, info->msg, len);
-		if (err)
-			goto out;
-
-		if (msg_data_left(info->msg) == 0 &&
-		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
-			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
-
-			if (info->msg->msg_flags & MSG_EOR)
-				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
-		}
-	}
+	hdr->len	= cpu_to_le32(payload_len);
+}
 
-	if (info->reply)
-		virtio_vsock_skb_set_reply(skb);
+static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb,
+						void *dst,
+						size_t len)
+{
+	struct iov_iter iov_iter = { 0 };
+	struct kvec kvec;
+	size_t to_copy;
 
-	trace_virtio_transport_alloc_pkt(src_cid, src_port,
-					 dst_cid, dst_port,
-					 len,
-					 info->type,
-					 info->op,
-					 info->flags);
+	kvec.iov_base = dst;
+	kvec.iov_len = len;
 
-	if (info->vsk && !skb_set_owner_sk_safe(skb, sk_vsock(info->vsk))) {
-		WARN_ONCE(1, "failed to allocate skb on vsock socket with sk_refcnt == 0\n");
-		goto out;
-	}
+	iov_iter.iter_type = ITER_KVEC;
+	iov_iter.kvec = &kvec;
+	iov_iter.nr_segs = 1;
 
-	return skb;
+	to_copy = min_t(size_t, len, skb->len);
 
-out:
-	kfree_skb(skb);
-	return NULL;
+	skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->offset,
+			       &iov_iter, to_copy);
 }
 
 /* Packet capture */
@@ -114,7 +161,6 @@ static struct sk_buff *virtio_transport_build_skb(void *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
@@ -122,7 +168,6 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	 */
 	pkt_hdr = virtio_vsock_hdr(pkt);
 	payload_len = pkt->len;
-	payload_buf = pkt->data;
 
 	skb = alloc_skb(sizeof(*hdr) + sizeof(*pkt_hdr) + payload_len,
 			GFP_ATOMIC);
@@ -165,7 +210,13 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque)
 	skb_put_data(skb, pkt_hdr, sizeof(*pkt_hdr));
 
 	if (payload_len) {
-		skb_put_data(skb, payload_buf, payload_len);
+		if (skb_is_nonlinear(pkt)) {
+			void *data = skb_put(skb, payload_len);
+
+			virtio_transport_copy_nonlinear_skb(pkt, data, payload_len);
+		} else {
+			skb_put_data(skb, pkt->data, payload_len);
+		}
 	}
 
 	return skb;
@@ -189,6 +240,82 @@ static u16 virtio_transport_get_type(struct sock *sk)
 		return VIRTIO_VSOCK_TYPE_SEQPACKET;
 }
 
+/* Returns new sk_buff on success, otherwise returns NULL. */
+static struct sk_buff *virtio_transport_alloc_skb(struct virtio_vsock_pkt_info *info,
+						  size_t payload_len,
+						  bool zcopy,
+						  u32 src_cid,
+						  u32 src_port,
+						  u32 dst_cid,
+						  u32 dst_port)
+{
+	struct vsock_sock *vsk;
+	struct sk_buff *skb;
+	size_t skb_len;
+
+	skb_len = VIRTIO_VSOCK_SKB_HEADROOM;
+
+	if (!zcopy)
+		skb_len += payload_len;
+
+	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	virtio_transport_init_hdr(skb, info, payload_len, src_cid, src_port,
+				  dst_cid, dst_port);
+
+	vsk = info->vsk;
+
+	/* If 'vsk' != NULL then payload is always present, so we
+	 * will never call '__zerocopy_sg_from_iter()' below without
+	 * setting skb owner in 'skb_set_owner_w()'. The only case
+	 * when 'vsk' == NULL is VIRTIO_VSOCK_OP_RST control message
+	 * without payload.
+	 */
+	WARN_ON_ONCE(!(vsk && (info->msg && payload_len)) && zcopy);
+
+	/* Set owner here, because '__zerocopy_sg_from_iter()' uses
+	 * owner of skb without check to update 'sk_wmem_alloc'.
+	 */
+	if (vsk)
+		skb_set_owner_w(skb, sk_vsock(vsk));
+
+	if (info->msg && payload_len > 0) {
+		int err;
+
+		err = virtio_transport_fill_skb(skb, info, payload_len, zcopy);
+		if (err)
+			goto out;
+
+		if (msg_data_left(info->msg) == 0 &&
+		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
+			struct virtio_vsock_hdr *hdr = virtio_vsock_hdr(skb);
+
+			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
+
+			if (info->msg->msg_flags & MSG_EOR)
+				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
+		}
+	}
+
+	if (info->reply)
+		virtio_vsock_skb_set_reply(skb);
+
+	trace_virtio_transport_alloc_pkt(src_cid, src_port,
+					 dst_cid, dst_port,
+					 payload_len,
+					 info->type,
+					 info->op,
+					 info->flags,
+					 zcopy);
+
+	return skb;
+out:
+	kfree_skb(skb);
+	return NULL;
+}
+
 /* This function can only be used on connecting/connected sockets,
  * since a socket assigned to a transport is required.
  *
@@ -197,10 +324,12 @@ static u16 virtio_transport_get_type(struct sock *sk)
 static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 					  struct virtio_vsock_pkt_info *info)
 {
+	u32 max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
 	u32 src_cid, src_port, dst_cid, dst_port;
 	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	u32 pkt_len = info->pkt_len;
+	bool can_zcopy = false;
 	u32 rest_len;
 	int ret;
 
@@ -229,15 +358,30 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
 		return pkt_len;
 
+	if (info->msg) {
+		/* If zerocopy is not enabled by 'setsockopt()', we behave as
+		 * there is no MSG_ZEROCOPY flag set.
+		 */
+		if (!sock_flag(sk_vsock(vsk), SOCK_ZEROCOPY))
+			info->msg->msg_flags &= ~MSG_ZEROCOPY;
+
+		if (info->msg->msg_flags & MSG_ZEROCOPY)
+			can_zcopy = virtio_transport_can_zcopy(t_ops, info, pkt_len);
+
+		if (can_zcopy)
+			max_skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE,
+					    (MAX_SKB_FRAGS * PAGE_SIZE));
+	}
+
 	rest_len = pkt_len;
 
 	do {
 		struct sk_buff *skb;
 		size_t skb_len;
 
-		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
+		skb_len = min(max_skb_len, rest_len);
 
-		skb = virtio_transport_alloc_skb(info, skb_len,
+		skb = virtio_transport_alloc_skb(info, skb_len, can_zcopy,
 						 src_cid, src_port,
 						 dst_cid, dst_port);
 		if (!skb) {
@@ -245,6 +389,21 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 			break;
 		}
 
+		/* We process buffer part by part, allocating skb on
+		 * each iteration. If this is last skb for this buffer
+		 * and MSG_ZEROCOPY mode is in use - we must allocate
+		 * completion for the current syscall.
+		 */
+		if (info->msg && info->msg->msg_flags & MSG_ZEROCOPY &&
+		    skb_len == rest_len && info->op == VIRTIO_VSOCK_OP_RW) {
+			if (virtio_transport_init_zcopy_skb(vsk, skb,
+							    info->msg,
+							    can_zcopy)) {
+				ret = -ENOMEM;
+				break;
+			}
+		}
+
 		virtio_transport_inc_tx_pkt(vvs, skb);
 
 		ret = t_ops->send_pkt(skb);
@@ -364,9 +523,10 @@ virtio_transport_stream_do_peek(struct vsock_sock *vsk,
 		spin_unlock_bh(&vvs->rx_lock);
 
 		/* sk_lock is held by caller so no one else can dequeue.
-		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 		 */
-		err = memcpy_to_msg(msg, skb->data, bytes);
+		err = skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->offset,
+					     &msg->msg_iter, bytes);
 		if (err)
 			goto out;
 
@@ -410,25 +570,27 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	while (total < len && !skb_queue_empty(&vvs->rx_queue)) {
 		skb = skb_peek(&vvs->rx_queue);
 
-		bytes = len - total;
-		if (bytes > skb->len)
-			bytes = skb->len;
+		bytes = min_t(size_t, len - total,
+			      skb->len - VIRTIO_VSOCK_SKB_CB(skb)->offset);
 
 		/* sk_lock is held by caller so no one else can dequeue.
-		 * Unlock rx_lock since memcpy_to_msg() may sleep.
+		 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 		 */
 		spin_unlock_bh(&vvs->rx_lock);
 
-		err = memcpy_to_msg(msg, skb->data, bytes);
+		err = skb_copy_datagram_iter(skb,
+					     VIRTIO_VSOCK_SKB_CB(skb)->offset,
+					     &msg->msg_iter, bytes);
 		if (err)
 			goto out;
 
 		spin_lock_bh(&vvs->rx_lock);
 
 		total += bytes;
-		skb_pull(skb, bytes);
 
-		if (skb->len == 0) {
+		VIRTIO_VSOCK_SKB_CB(skb)->offset += bytes;
+
+		if (skb->len == VIRTIO_VSOCK_SKB_CB(skb)->offset) {
 			u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
 
 			virtio_transport_dec_rx_pkt(vvs, pkt_len);
@@ -492,9 +654,10 @@ virtio_transport_seqpacket_do_peek(struct vsock_sock *vsk,
 			spin_unlock_bh(&vvs->rx_lock);
 
 			/* sk_lock is held by caller so no one else can dequeue.
-			 * Unlock rx_lock since memcpy_to_msg() may sleep.
+			 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 			 */
-			err = memcpy_to_msg(msg, skb->data, bytes);
+			err = skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->offset,
+						     &msg->msg_iter, bytes);
 			if (err)
 				return err;
 
@@ -553,11 +716,13 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
 				int err;
 
 				/* sk_lock is held by caller so no one else can dequeue.
-				 * Unlock rx_lock since memcpy_to_msg() may sleep.
+				 * Unlock rx_lock since skb_copy_datagram_iter() may sleep.
 				 */
 				spin_unlock_bh(&vvs->rx_lock);
 
-				err = memcpy_to_msg(msg, skb->data, bytes_to_copy);
+				err = skb_copy_datagram_iter(skb, 0,
+							     &msg->msg_iter,
+							     bytes_to_copy);
 				if (err) {
 					/* Copy of message failed. Rest of
 					 * fragments will be freed without copy.
@@ -954,7 +1119,7 @@ static int virtio_transport_reset_no_sock(const struct virtio_transport *t,
 	if (!t)
 		return -ENOTCONN;
 
-	reply = virtio_transport_alloc_skb(&info, 0,
+	reply = virtio_transport_alloc_skb(&info, 0, false,
 					   le64_to_cpu(hdr->dst_cid),
 					   le32_to_cpu(hdr->dst_port),
 					   le64_to_cpu(hdr->src_cid),