ipv6: sr: fix seg6 encap performances with TSO enabled

Enabling TSO can lead to abysmal performances when using seg6 in
encap mode, such as with the ixgbe driver. This patch adds a call to
iptunnel_handle_offloads() to remove the encapsulation bit if needed.

Before:
root@comp4-seg6bpf:~# iperf3 -c fc00::55
Connecting to host fc00::55, port 5201
[  4] local fc45::4 port 36592 connected to fc00::55 port 5201
[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  4]   0.00-1.00   sec   196 KBytes  1.60 Mbits/sec   47   6.66 KBytes
[  4]   1.00-2.00   sec   304 KBytes  2.49 Mbits/sec  100   5.33 KBytes
[  4]   2.00-3.00   sec   284 KBytes  2.32 Mbits/sec   92   5.33 KBytes

After:
root@comp4-seg6bpf:~# iperf3 -c fc00::55
Connecting to host fc00::55, port 5201
[  4] local fc45::4 port 43062 connected to fc00::55 port 5201
[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  4]   0.00-1.00   sec  1.03 GBytes  8.89 Gbits/sec    0    743 KBytes
[  4]   1.00-2.00   sec  1.03 GBytes  8.87 Gbits/sec    0    743 KBytes
[  4]   2.00-3.00   sec  1.03 GBytes  8.87 Gbits/sec    0    743 KBytes

Reported-by: Tom Herbert <tom@quantonium.net>
Fixes: 6c8702c ("ipv6: sr: add support for SRH encapsulation and injection with lwtunnels")
Signed-off-by: David Lebrun <dlebrun@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/seg6_iptunnel.c

@@ -16,6 +16,7 @@
 #include <linux/net.h>
 #include <linux/module.h>
 #include <net/ip.h>
+#include <net/ip_tunnels.h>
 #include <net/lwtunnel.h>
 #include <net/netevent.h>
 #include <net/netns/generic.h>
@@ -211,11 +212,6 @@ static int seg6_do_srh(struct sk_buff *skb)
 
 	tinfo = seg6_encap_lwtunnel(dst->lwtstate);
 
-	if (likely(!skb->encapsulation)) {
-		skb_reset_inner_headers(skb);
-		skb->encapsulation = 1;
-	}
-
 	switch (tinfo->mode) {
 	case SEG6_IPTUN_MODE_INLINE:
 		if (skb->protocol != htons(ETH_P_IPV6))
@@ -224,10 +220,12 @@ static int seg6_do_srh(struct sk_buff *skb)
 		err = seg6_do_srh_inline(skb, tinfo->srh);
 		if (err)
 			return err;
-
-		skb_reset_inner_headers(skb);
 		break;
 	case SEG6_IPTUN_MODE_ENCAP:
+		err = iptunnel_handle_offloads(skb, SKB_GSO_IPXIP6);
+		if (err)
+			return err;
+
 		if (skb->protocol == htons(ETH_P_IPV6))
 			proto = IPPROTO_IPV6;
 		else if (skb->protocol == htons(ETH_P_IP))
@@ -239,6 +237,8 @@ static int seg6_do_srh(struct sk_buff *skb)
 		if (err)
 			return err;
 
+		skb_set_inner_transport_header(skb, skb_transport_offset(skb));
+		skb_set_inner_protocol(skb, skb->protocol);
 		skb->protocol = htons(ETH_P_IPV6);
 		break;
 	case SEG6_IPTUN_MODE_L2ENCAP:
@@ -262,8 +262,6 @@ static int seg6_do_srh(struct sk_buff *skb)
 	ipv6_hdr(skb)->payload_len = htons(skb->len - sizeof(struct ipv6hdr));
 	skb_set_transport_header(skb, sizeof(struct ipv6hdr));
 
-	skb_set_inner_protocol(skb, skb->protocol);
-
 	return 0;
 }