On 22.05.2023 16:09, Arseniy Krasnov wrote:

On 22.05.2023 16:11, Simon Horman wrote:

quoted

On Mon, May 22, 2023 at 10:39:38AM +0300, Arseniy Krasnov wrote:

quoted

This adds handling of MSG_ZEROCOPY flag on transmission path: if this
flag is set and zerocopy transmission is possible, then non-linear skb
will be created and filled with the pages of user's buffer. Pages of
user's buffer are locked in memory by 'get_user_pages()'.

Signed-off-by: Arseniy Krasnov <redacted>
---
 net/vmw_vsock/virtio_transport_common.c | 305 +++++++++++++++++++-----
 1 file changed, 243 insertions(+), 62 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 9854f48a0544..5acf824afe41 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c

@@ -37,73 +37,161 @@ 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(struct virtio_vsock_pkt_info *info,
+				       size_t max_to_send)
+{
+	struct iov_iter *iov_iter;
+	size_t max_skb_cap;
+	size_t bytes;
+	int i;
 
-	skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
-	if (!skb)
-		return NULL;
+	if (!info->msg)
+		return false;
 
-	hdr = virtio_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);
+	if (!(info->flags & MSG_ZEROCOPY) && !info->msg->msg_ubuf)
+		return false;
 
-	if (info->msg && len > 0) {
-		payload = skb_put(skb, len);
-		err = memcpy_from_msg(payload, info->msg, len);
-		if (err)
-			goto out;
+	iov_iter = &info->msg->msg_iter;
+
+	if (iter_is_ubuf(iov_iter)) {
+		if (offset_in_page(iov_iter->ubuf))
+			return false;
+
+		return true;
+	}
+
+	if (!iter_is_iovec(iov_iter))
+		return false;
+
+	if (iov_iter->iov_offset)
+		return false;
+
+	/* We can't send whole iov. */
+	if (iov_iter->count > max_to_send)
+		return false;
+
+	for (bytes = 0, i = 0; i < iov_iter->nr_segs; i++) {
+		const struct iovec *iovec;
+		int pages_in_elem;
+
+		iovec = &iov_iter->__iov[i];
+
+		/* Base must be page aligned. */
+		if (offset_in_page(iovec->iov_base))
+			return false;
 
-		if (msg_data_left(info->msg) == 0 &&
-		    info->type == VIRTIO_VSOCK_TYPE_SEQPACKET) {
-			hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOM);
+		/* Only last element could have non page aligned size. */
+		if (i != (iov_iter->nr_segs - 1)) {
+			if (offset_in_page(iovec->iov_len))
+				return false;
 
-			if (info->msg->msg_flags & MSG_EOR)
-				hdr->flags |= cpu_to_le32(VIRTIO_VSOCK_SEQ_EOR);
+			pages_in_elem = iovec->iov_len >> PAGE_SHIFT;
+		} else {
+			pages_in_elem = round_up(iovec->iov_len, PAGE_SIZE);
+			pages_in_elem >>= PAGE_SHIFT;
 		}
+
+		bytes += (pages_in_elem * PAGE_SIZE);

^^^
This alignment (base and length) checks are not needed, because virtio supports unaligned buffers. I'll remove
it in v4.

Thanks, Arseniy

quoted

quoted

 	}

Hi Arseniy,

bytes is set but the loop above, but seems otherwise unused in this function.

quoted

 
-	if (info->reply)
-		virtio_vsock_skb_set_reply(skb);
+	/* How many bytes we can pack to single skb. Maximum packet
+	 * buffer size is needed to allow vhost handle such packets,
+	 * otherwise they will be dropped.
+	 */
+	max_skb_cap = min((unsigned int)(MAX_SKB_FRAGS * PAGE_SIZE),
+			  (unsigned int)VIRTIO_VSOCK_MAX_PKT_BUF_SIZE);

Likewise, max_skb_cap seems to be set but unused in this function.

Exactly! Seems I forgot to remove it since v2. Thanks for this and above!

quoted

quoted

 
-	trace_virtio_transport_alloc_pkt(src_cid, src_port,
-					 dst_cid, dst_port,
-					 len,
-					 info->type,
-					 info->op,
-					 info->flags);
+	return true;
+}

...