ila: Precompute checksum difference for translations

In the ILA build state for LWT compute the checksum difference to apply
to transport checksums that include the IPv6 pseudo header. The
difference is between the route destination (from fib6_config) and the
locator to write.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ila.c

@@ -14,6 +14,8 @@
 
 struct ila_params {
 	__be64 locator;
+	__be64 locator_match;
+	__wsum csum_diff;
 };
 
 static inline struct ila_params *ila_params_lwtunnel(
@@ -33,6 +35,9 @@ static inline __wsum compute_csum_diff8(const __be32 *from, const __be32 *to)
 
 static inline __wsum get_csum_diff(struct ipv6hdr *ip6h, struct ila_params *p)
 {
+	if (*(__be64 *)&ip6h->daddr == p->locator_match)
+		return p->csum_diff;
+	else
 		return compute_csum_diff8((__be32 *)&ip6h->daddr,
 					  (__be32 *)&p->locator);
 }
@@ -130,8 +135,12 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 	struct nlattr *tb[ILA_ATTR_MAX + 1];
 	size_t encap_len = sizeof(*p);
 	struct lwtunnel_state *newts;
+	const struct fib6_config *cfg6 = cfg;
 	int ret;
 
+	if (family != AF_INET6)
+		return -EINVAL;
+
 	ret = nla_parse_nested(tb, ILA_ATTR_MAX, nla,
 			       ila_nl_policy);
 	if (ret < 0)
@@ -149,6 +158,15 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 
 	p->locator = (__force __be64)nla_get_u64(tb[ILA_ATTR_LOCATOR]);
 
+	if (cfg6->fc_dst_len > sizeof(__be64)) {
+		/* Precompute checksum difference for translation since we
+		 * know both the old locator and the new one.
+		 */
+		p->locator_match = *(__be64 *)&cfg6->fc_dst;
+		p->csum_diff = compute_csum_diff8(
+			(__be32 *)&p->locator_match, (__be32 *)&p->locator);
+	}
+
 	newts->type = LWTUNNEL_ENCAP_ILA;
 	newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT |
 			LWTUNNEL_STATE_INPUT_REDIRECT;