[PATCH RFC 7/8] vsock: preserve host-to-guest datagram boundaries

[Sergio Lopez <slp@redhat.com>]

Vhost splits large datagrams across guest RX buffers, delivering each
fragment as a separate message. Allocate full-size RX buffers with
page fragments when datagrams are negotiated, and drop whole datagrams
if a guest buffer is too small. Refill empty RX queues even when only
one full-size buffer fits in the ring.

Signed-off-by: Sergio Lopez <slp@redhat.com>
---
 drivers/vhost/vsock.c            |  8 ++++++++
 net/vmw_vsock/virtio_transport.c | 28 +++++++++++++++++++---------
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 79ffdb28f4d9..2294ed8d30a8 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -185,6 +185,14 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
 		 * buffer, we split it using multiple buffers.
 		 */
 		if (payload_len > iov_len - sizeof(*hdr)) {
+			/* Datagrams must fit in a single descriptor chain. */
+			if (le16_to_cpu(hdr->type) == VIRTIO_VSOCK_TYPE_DGRAM) {
+				kfree_skb(skb);
+				vhost_add_used(vq, head, 0);
+				added = true;
+				continue;
+			}
+
 			payload_len = iov_len - sizeof(*hdr);
 
 			/* As we are copying pieces of large packet's buffer to
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 14ce0836bc39..d256274088b3 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -54,6 +54,7 @@ struct virtio_vsock {
 	bool rx_run;
 	int rx_buf_nr;
 	int rx_buf_max_nr;
+	struct scatterlist in_bufs[MAX_SKB_FRAGS + 1];
 
 	u32 guest_cid;
 	bool seqpacket_allow;
@@ -312,22 +313,31 @@ virtio_transport_cancel_pkt(struct vsock_sock *vsk)
 static void virtio_vsock_rx_fill(struct virtio_vsock *vsock)
 {
 	int total_len = VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE;
-	struct scatterlist pkt, *p;
 	struct virtqueue *vq;
 	struct sk_buff *skb;
 	int ret;
 
 	vq = vsock->vqs[VSOCK_VQ_RX];
+	/* A datagram must fit in one RX buffer, including its header. */
+	if (vsock->dgram_allow)
+		total_len = VIRTIO_VSOCK_SKB_HEADROOM +
+			    VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
 
 	do {
-		skb = virtio_vsock_alloc_linear_skb(total_len, GFP_KERNEL);
+		skb = virtio_vsock_alloc_skb(total_len, GFP_KERNEL);
 		if (!skb)
 			break;
 
 		memset(skb->head, 0, VIRTIO_VSOCK_SKB_HEADROOM);
-		sg_init_one(&pkt, virtio_vsock_hdr(skb), total_len);
-		p = &pkt;
-		ret = virtqueue_add_sgs(vq, &p, 0, 1, skb, GFP_KERNEL);
+		/* Post the header and the entire payload as one RX buffer. */
+		virtio_vsock_skb_put(skb, total_len - VIRTIO_VSOCK_SKB_HEADROOM);
+		skb_push(skb, VIRTIO_VSOCK_SKB_HEADROOM);
+		sg_init_table(vsock->in_bufs, ARRAY_SIZE(vsock->in_bufs));
+		ret = skb_to_sgvec(skb, vsock->in_bufs, 0, total_len);
+		skb_pull(skb, VIRTIO_VSOCK_SKB_HEADROOM);
+		if (ret >= 0)
+			ret = virtqueue_add_inbuf(vq, vsock->in_bufs, ret, skb,
+						  GFP_KERNEL);
 		if (ret < 0) {
 			kfree_skb(skb);
 			break;
@@ -698,7 +708,7 @@ static void virtio_transport_rx_work(struct work_struct *work)
 
 			/* Drop short/long packets */
 			if (unlikely(len < sizeof(*hdr) ||
-				     len > virtio_vsock_skb_len(skb))) {
+				     len > sizeof(*hdr) + skb->len)) {
 				kfree_skb(skb);
 				continue;
 			}
@@ -710,8 +720,7 @@ static void virtio_transport_rx_work(struct work_struct *work)
 				continue;
 			}
 
-			if (payload_len)
-				virtio_vsock_skb_put(skb, payload_len);
+			pskb_trim_unique(skb, payload_len);
 
 			virtio_transport_deliver_tap_pkt(skb);
 
@@ -723,7 +732,8 @@ static void virtio_transport_rx_work(struct work_struct *work)
 	} while (!virtqueue_enable_cb(vq));
 
 out:
-	if (vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2)
+	if (!vsock->rx_buf_nr ||
+	    vsock->rx_buf_nr < vsock->rx_buf_max_nr / 2)
 		virtio_vsock_rx_fill(vsock);
 out_nofill:
 	mutex_unlock(&vsock->rx_lock);

-- 
2.56.0