ibmveth: Identify ingress large send packets.

Ingress large send packets are identified by either:
The IBMVETH_RXQ_LRG_PKT flag in the receive buffer
or with a -1 placed in the ip header checksum.
The method used depends on firmware version. Frame
geometry and sufficient header validation is performed by the
hypervisor eliminating the need for further header checks here.

Fixes: 7b596738 ("ibmveth: set correct gso_size and gso_type")
Signed-off-by: David Wilder <dwilder@us.ibm.com>
Reviewed-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Reviewed-by: Cristobal Forno <cris.forno@ibm.com>
Reviewed-by: Pradeep Satyanarayana <pradeeps@linux.vnet.ibm.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/ibm/ibmveth.c

@@ -1349,6 +1349,7 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
 			int offset = ibmveth_rxq_frame_offset(adapter);
 			int csum_good = ibmveth_rxq_csum_good(adapter);
 			int lrg_pkt = ibmveth_rxq_large_packet(adapter);
+			__sum16 iph_check = 0;
 
 			skb = ibmveth_rxq_get_buffer(adapter);
 
@@ -1385,7 +1386,17 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
 			skb_put(skb, length);
 			skb->protocol = eth_type_trans(skb, netdev);
 
-			if (length > netdev->mtu + ETH_HLEN) {
+			/* PHYP without PLSO support places a -1 in the ip
+			 * checksum for large send frames.
+			 */
+			if (skb->protocol == cpu_to_be16(ETH_P_IP)) {
+				struct iphdr *iph = (struct iphdr *)skb->data;
+
+				iph_check = iph->check;
+			}
+
+			if ((length > netdev->mtu + ETH_HLEN) ||
+			    lrg_pkt || iph_check == 0xffff) {
 				ibmveth_rx_mss_helper(skb, mss, lrg_pkt);
 				adapter->rx_large_packets++;
 			}