vsock/virtio: Move length check to callers of virtio_vsock_skb_rx_put()

virtio_vsock_skb_rx_put() only calls skb_put() if the length in the
packet header is not zero even though skb_put() handles this case
gracefully.

Remove the functionally redundant check from virtio_vsock_skb_rx_put()
and, on the assumption that this is a worthwhile optimisation for
handling credit messages, augment the existing length checks in
virtio_transport_rx_work() to elide the call for zero-length payloads.
Since the callers all have the length, extend virtio_vsock_skb_rx_put()
to take it as an additional parameter rather than fish it back out of
the packet header.

Note that the vhost code already has similar logic in
vhost_vsock_alloc_skb().

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
Message-Id: <20250717090116.11987-4-will@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Author: willdeacon

drivers/vhost/vsock.c

@@ -375,7 +375,7 @@ vhost_vsock_alloc_skb(struct vhost_virtqueue *vq,
 		return NULL;
 	}
 
-	virtio_vsock_skb_rx_put(skb);
+	virtio_vsock_skb_rx_put(skb, payload_len);
 
 	nbytes = copy_from_iter(skb->data, payload_len, &iov_iter);
 	if (nbytes != payload_len) {

include/linux/virtio_vsock.h

@@ -47,14 +47,9 @@ static inline void virtio_vsock_skb_clear_tap_delivered(struct sk_buff *skb)
 	VIRTIO_VSOCK_SKB_CB(skb)->tap_delivered = false;
 }
 
-static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb)
+static inline void virtio_vsock_skb_rx_put(struct sk_buff *skb, u32 len)
 {
-	u32 len;
-
-	len = le32_to_cpu(virtio_vsock_hdr(skb)->len);
-
-	if (len > 0)
-		skb_put(skb, len);
+	skb_put(skb, len);
 }
 
 static inline struct sk_buff *virtio_vsock_alloc_skb(unsigned int size, gfp_t mask)

net/vmw_vsock/virtio_transport.c

@@ -656,7 +656,9 @@ static void virtio_transport_rx_work(struct work_struct *work)
 				continue;
 			}
 
-			virtio_vsock_skb_rx_put(skb);
+			if (payload_len)
+				virtio_vsock_skb_rx_put(skb, payload_len);
+
 			virtio_transport_deliver_tap_pkt(skb);
 			virtio_transport_recv_pkt(&virtio_transport, skb);
 		}