ipv6: Support multipath hashing on inner IP pkts

Make the same support as commit 363887a2 ("ipv4: Support multipath
hashing on inner IP pkts for GRE tunnel") for outer IPv6. The hashing
considers both IPv4 and IPv6 pkts when they are tunneled by IPv6 GRE.
Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1473,6 +1473,7 @@ fib_multipath_hash_policy - INTEGER
 	Possible values:
 	0 - Layer 3 (source and destination addresses plus flow label)
 	1 - Layer 4 (standard 5-tuple)
+	2 - Layer 3 or inner Layer 3 if present
 
 anycast_src_echo_reply - BOOLEAN
 	Controls the use of anycast addresses as source addresses for ICMPv6

net/ipv6/route.c

@@ -2370,6 +2370,42 @@ u32 rt6_multipath_hash(const struct net *net, const struct flowi6 *fl6,
 			hash_keys.basic.ip_proto = fl6->flowi6_proto;
 		}
 		break;
+	case 2:
+		memset(&hash_keys, 0, sizeof(hash_keys));
+		hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
+		if (skb) {
+			struct flow_keys keys;
+
+			if (!flkeys) {
+				skb_flow_dissect_flow_keys(skb, &keys, 0);
+				flkeys = &keys;
+			}
+
+			/* Inner can be v4 or v6 */
+			if (flkeys->control.addr_type == FLOW_DISSECTOR_KEY_IPV4_ADDRS) {
+				hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV4_ADDRS;
+				hash_keys.addrs.v4addrs.src = flkeys->addrs.v4addrs.src;
+				hash_keys.addrs.v4addrs.dst = flkeys->addrs.v4addrs.dst;
+			} else if (flkeys->control.addr_type == FLOW_DISSECTOR_KEY_IPV6_ADDRS) {
+				hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
+				hash_keys.addrs.v6addrs.src = flkeys->addrs.v6addrs.src;
+				hash_keys.addrs.v6addrs.dst = flkeys->addrs.v6addrs.dst;
+				hash_keys.tags.flow_label = flkeys->tags.flow_label;
+				hash_keys.basic.ip_proto = flkeys->basic.ip_proto;
+			} else {
+				/* Same as case 0 */
+				hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
+				ip6_multipath_l3_keys(skb, &hash_keys, flkeys);
+			}
+		} else {
+			/* Same as case 0 */
+			hash_keys.control.addr_type = FLOW_DISSECTOR_KEY_IPV6_ADDRS;
+			hash_keys.addrs.v6addrs.src = fl6->saddr;
+			hash_keys.addrs.v6addrs.dst = fl6->daddr;
+			hash_keys.tags.flow_label = (__force u32)flowi6_get_flowlabel(fl6);
+			hash_keys.basic.ip_proto = fl6->flowi6_proto;
+		}
+		break;
 	}
 	mhash = flow_hash_from_keys(&hash_keys);