Drivers: net: hyperv: Address UDP checksum issues

ws2008r2 does not support UDP checksum offload. Thus, we cannnot turn on
UDP offload in the host. Also, on ws2012 and ws2012 r2, there appear to be
an issue with UDP checksum offload.
Fix this issue by computing the UDP checksum in the Hyper-V driver.

Based on Dave Miller's comments, in this version, I have COWed the skb
before modifying the UDP header (the checksum field).
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: NHaiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -747,6 +747,7 @@ struct ndis_oject_header {
 #define NDIS_TCP_LARGE_SEND_OFFLOAD_IPV4	0
 #define NDIS_TCP_LARGE_SEND_OFFLOAD_IPV6	1
 
+#define VERSION_4_OFFLOAD_SIZE			22
 /*
  * New offload OIDs for NDIS 6
  */

drivers/net/hyperv/netvsc_drv.c

@@ -398,7 +398,30 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 		csum_info->transmit.tcp_checksum = 1;
 		csum_info->transmit.tcp_header_offset = hdr_offset;
 	} else if (net_trans_info & INFO_UDP) {
-		csum_info->transmit.udp_checksum = 1;
+		/* UDP checksum offload is not supported on ws2008r2.
+		 * Furthermore, on ws2012 and ws2012r2, there are some
+		 * issues with udp checksum offload from Linux guests.
+		 * (these are host issues).
+		 * For now compute the checksum here.
+		 */
+		struct udphdr *uh;
+		u16 udp_len;
+
+		ret = skb_cow_head(skb, 0);
+		if (ret)
+			goto drop;
+
+		uh = udp_hdr(skb);
+		udp_len = ntohs(uh->len);
+		uh->check = 0;
+		uh->check = csum_tcpudp_magic(ip_hdr(skb)->saddr,
+					      ip_hdr(skb)->daddr,
+					      udp_len, IPPROTO_UDP,
+					      csum_partial(uh, udp_len, 0));
+		if (uh->check == 0)
+			uh->check = CSUM_MANGLED_0;
+
+		csum_info->transmit.udp_checksum = 0;
 	}
 	goto do_send;
 
@@ -438,6 +461,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 
 	ret = netvsc_send(net_device_ctx->device_ctx, packet);
 
+drop:
 	if (ret == 0) {
 		net->stats.tx_bytes += skb->len;
 		net->stats.tx_packets++;

drivers/net/hyperv/rndis_filter.c

@@ -641,6 +641,16 @@ int rndis_filter_set_offload_params(struct hv_device *hdev,
 	struct rndis_set_complete *set_complete;
 	u32 extlen = sizeof(struct ndis_offload_params);
 	int ret, t;
+	u32 vsp_version = nvdev->nvsp_version;
+
+	if (vsp_version <= NVSP_PROTOCOL_VERSION_4) {
+		extlen = VERSION_4_OFFLOAD_SIZE;
+		/* On NVSP_PROTOCOL_VERSION_4 and below, we do not support
+		 * UDP checksum offload.
+		 */
+		req_offloads->udp_ip_v4_csum = 0;
+		req_offloads->udp_ip_v6_csum = 0;
+	}
 
 	request = get_rndis_request(rdev, RNDIS_MSG_SET,
 		RNDIS_MESSAGE_SIZE(struct rndis_set_request) + extlen);
@@ -674,7 +684,7 @@ int rndis_filter_set_offload_params(struct hv_device *hdev,
 	} else {
 		set_complete = &request->response_msg.msg.set_complete;
 		if (set_complete->status != RNDIS_STATUS_SUCCESS) {
-			netdev_err(ndev, "Fail to set MAC on host side:0x%x\n",
+			netdev_err(ndev, "Fail to set offload on host side:0x%x\n",
 				   set_complete->status);
 			ret = -EINVAL;
 		}