gue: TX support for using remote checksum offload option

Add if_tunnel flag TUNNEL_ENCAP_FLAG_REMCSUM to configure
remote checksum offload on an IP tunnel. Add logic in gue_build_header
to insert remote checksum offload option.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 46 insertions, 4 deletions

diff --git a/include/net/fou.h b/include/net/fou.h
index cf4ce8874f92..25b26ffcf1df 100644
--- a/include/net/fou.h
+++ b/include/net/fou.h
@@ -20,7 +20,19 @@ static size_t fou_encap_hlen(struct ip_tunnel_encap *e)
 
 static size_t gue_encap_hlen(struct ip_tunnel_encap *e)
 {
-        return sizeof(struct udphdr) + sizeof(struct guehdr);
+        size_t len;
+        bool need_priv = false;
+
+        len = sizeof(struct udphdr) + sizeof(struct guehdr);
+
+        if (e->flags & TUNNEL_ENCAP_FLAG_REMCSUM) {
+                len += GUE_PLEN_REMCSUM;
+                need_priv = true;
+        }
+
+        len += need_priv ? GUE_LEN_PRIV : 0;
+
+        return len;
 }
 
 #endif
diff --git a/include/uapi/linux/if_tunnel.h b/include/uapi/linux/if_tunnel.h
index 280d9e092283..bd3cc11a431f 100644
--- a/include/uapi/linux/if_tunnel.h
+++ b/include/uapi/linux/if_tunnel.h
@@ -69,6 +69,7 @@ enum tunnel_encap_types {
 
 #define TUNNEL_ENCAP_FLAG_CSUM          (1<<0)
 #define TUNNEL_ENCAP_FLAG_CSUM6         (1<<1)
+#define TUNNEL_ENCAP_FLAG_REMCSUM       (1<<2)
 
 /* SIT-mode i_flags */
 #define SIT_ISATAP      0x0001
diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index a3b8c5b36303..fb0db99adf9e 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -562,11 +562,19 @@ int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
         bool csum = !!(e->flags & TUNNEL_ENCAP_FLAG_CSUM);
         int type = csum ? SKB_GSO_UDP_TUNNEL_CSUM : SKB_GSO_UDP_TUNNEL;
         struct guehdr *guehdr;
-        size_t optlen = 0;
+        size_t hdrlen, optlen = 0;
         __be16 sport;
         void *data;
         bool need_priv = false;
 
+        if ((e->flags & TUNNEL_ENCAP_FLAG_REMCSUM) &&
+            skb->ip_summed == CHECKSUM_PARTIAL) {
+                csum = false;
+                optlen += GUE_PLEN_REMCSUM;
+                type |= SKB_GSO_TUNNEL_REMCSUM;
+                need_priv = true;
+        }
+
         optlen += need_priv ? GUE_LEN_PRIV : 0;
 
         skb = iptunnel_handle_offloads(skb, csum, type);
@@ -578,7 +586,9 @@ int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
         sport = e->sport ? : udp_flow_src_port(dev_net(skb->dev),
                                                skb, 0, 0, false);
 
-        skb_push(skb, sizeof(struct guehdr) + optlen);
+        hdrlen = sizeof(struct guehdr) + optlen;
+
+        skb_push(skb, hdrlen);
 
         guehdr = (struct guehdr *)skb->data;
 
@@ -597,7 +607,26 @@ int gue_build_header(struct sk_buff *skb, struct ip_tunnel_encap *e,
                 *flags = 0;
                 data += GUE_LEN_PRIV;
 
-                /* Add private flags */
+                if (type & SKB_GSO_TUNNEL_REMCSUM) {
+                        u16 csum_start = skb_checksum_start_offset(skb);
+                        __be16 *pd = data;
+
+                        if (csum_start < hdrlen)
+                                return -EINVAL;
+
+                        csum_start -= hdrlen;
+                        pd[0] = htons(csum_start);
+                        pd[1] = htons(csum_start + skb->csum_offset);
+
+                        if (!skb_is_gso(skb)) {
+                                skb->ip_summed = CHECKSUM_NONE;
+                                skb->encapsulation = 0;
+                        }
+
+                        *flags |= GUE_PFLAG_REMCSUM;
+                        data += GUE_PLEN_REMCSUM;
+                }
+
         }
 
         fou_build_udp(skb, e, fl4, protocol, sport);