ixgbe: Handle extended IPv6 headers in Tx path

BugLink: http://bugs.launchpad.net/bugs/1536473

Check for and handle IPv6 extended headers so that Tx checksum
offload can be done. Also use skb_checksum_help for unexpected
cases. Thanks to Tom Herbert for noticing these problems. Thanks
to Alexander Duyck for recognizing problems with the first version
of this patch and recognizing how to coalesce error conditions
into a single location.
Reported-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit 36a92d71)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -7063,6 +7063,7 @@ static void ixgbe_tx_csum(struct ixgbe_ring *tx_ring,
 			struct tcphdr *tcphdr;
 			u8 *raw;
 		} transport_hdr;
+		__be16 frag_off;
 
 		if (skb->encapsulation) {
 			network_hdr.raw = skb_inner_network_header(skb);
@@ -7086,13 +7087,17 @@ static void ixgbe_tx_csum(struct ixgbe_ring *tx_ring,
 		case 6:
 			vlan_macip_lens |= transport_hdr.raw - network_hdr.raw;
 			l4_hdr = network_hdr.ipv6->nexthdr;
+			if (likely((transport_hdr.raw - network_hdr.raw) ==
+				   sizeof(struct ipv6hdr)))
+				break;
+			ipv6_skip_exthdr(skb, network_hdr.raw - skb->data +
+					      sizeof(struct ipv6hdr),
+					 &l4_hdr, &frag_off);
+			if (unlikely(frag_off))
+				l4_hdr = NEXTHDR_FRAGMENT;
 			break;
 		default:
-			if (unlikely(net_ratelimit())) {
-				dev_warn(tx_ring->dev,
-					 "partial checksum but version=%d\n",
-					 network_hdr.ipv4->version);
-			}
+			break;
 		}
 
 		switch (l4_hdr) {
@@ -7113,16 +7118,18 @@ static void ixgbe_tx_csum(struct ixgbe_ring *tx_ring,
 		default:
 			if (unlikely(net_ratelimit())) {
 				dev_warn(tx_ring->dev,
-				 "partial checksum but l4 proto=%x!\n",
-				 l4_hdr);
+					 "partial checksum, version=%d, l4 proto=%x\n",
+					 network_hdr.ipv4->version, l4_hdr);
 			}
-			break;
+			skb_checksum_help(skb);
+			goto no_csum;
 		}
 
 		/* update TX checksum flag */
 		first->tx_flags |= IXGBE_TX_FLAGS_CSUM;
 	}
 
+no_csum:
 	/* vlan_macip_lens: MACLEN, VLAN tag */
 	vlan_macip_lens |= first->tx_flags & IXGBE_TX_FLAGS_VLAN_MASK;