ila: Perform only one translation in forwarding path

When setting up ILA in a router we noticed that the the encapsulation
is invoked twice: once in the route input path and again upon route
output. To resolve this we add a flag set_csum_neutral for the
ila_update_ipv6_locator. If this flag is set and the checksum
neutral bit is also set we assume that checksum-neutral translation
has already been performed and take no further action. The
flag is set only in ila_output path. The flag is not set for ila_input and
ila_xlat.

Tested:

Used 3 netns to set to emulate a router and two hosts. The router
translates SIR addresses between the two destinations in other two netns.
Verified ping and netperf are functional.

Signed-off-by: Tom Herbert <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv6/ila/ila.h

···
 	return !!(ident.csum_neutral);
 }
 
-void ila_update_ipv6_locator(struct sk_buff *skb, struct ila_params *p);
+void ila_update_ipv6_locator(struct sk_buff *skb, struct ila_params *p,
+			     bool set_csum_neutral);
 
 void ila_init_saved_csum(struct ila_params *p);
 

net/ipv6/ila/ila_common.c

···
 	iaddr->loc = p->locator;
 }
 
-void ila_update_ipv6_locator(struct sk_buff *skb, struct ila_params *p)
+void ila_update_ipv6_locator(struct sk_buff *skb, struct ila_params *p,
+			     bool set_csum_neutral)
 {
 	struct ipv6hdr *ip6h = ipv6_hdr(skb);
 	struct ila_addr *iaddr = ila_a2i(&ip6h->daddr);
···
 		 * is a locator being translated to a SIR address.
 		 * Perform (receiver) checksum-neutral translation.
 		 */
-		ila_csum_do_neutral(iaddr, p);
+		if (!set_csum_neutral)
+			ila_csum_do_neutral(iaddr, p);
 	} else {
 		switch (p->csum_mode) {
 		case ILA_CSUM_ADJUST_TRANSPORT:

net/ipv6/ila/ila_lwt.c

···
 	if (skb->protocol != htons(ETH_P_IPV6))
 		goto drop;
 
-	ila_update_ipv6_locator(skb, ila_params_lwtunnel(dst->lwtstate));
+	ila_update_ipv6_locator(skb, ila_params_lwtunnel(dst->lwtstate), true);
 
 	return dst->lwtstate->orig_output(net, sk, skb);
 
···
 	if (skb->protocol != htons(ETH_P_IPV6))
 		goto drop;
 
-	ila_update_ipv6_locator(skb, ila_params_lwtunnel(dst->lwtstate));
+	ila_update_ipv6_locator(skb, ila_params_lwtunnel(dst->lwtstate), false);
 
 	return dst->lwtstate->orig_input(skb);
 

net/ipv6/ila/ila_xlat.c

···
 	}
 }
 
-static int ila_xlat_addr(struct sk_buff *skb);
+static int ila_xlat_addr(struct sk_buff *skb, bool set_csum_neutral);
 
 static unsigned int
 ila_nf_input(void *priv,
 	     struct sk_buff *skb,
 	     const struct nf_hook_state *state)
 {
-	ila_xlat_addr(skb);
+	ila_xlat_addr(skb, false);
 	return NF_ACCEPT;
 }
 
···
 	.size = sizeof(struct ila_net),
 };
 
-static int ila_xlat_addr(struct sk_buff *skb)
+static int ila_xlat_addr(struct sk_buff *skb, bool set_csum_neutral)
 {
 	struct ila_map *ila;
 	struct ipv6hdr *ip6h = ipv6_hdr(skb);
···
 
 	ila = ila_lookup_wildcards(iaddr, skb->dev->ifindex, ilan);
 	if (ila)
-		ila_update_ipv6_locator(skb, &ila->xp.ip);
+		ila_update_ipv6_locator(skb, &ila->xp.ip, set_csum_neutral);
 
 	rcu_read_unlock();