GRE: Disable segmentation offloads w/ CSUM and we are encapsulated via FOU

This patch fixes an issue I found in which we were dropping frames if we
had enabled checksums on GRE headers that were encapsulated by either FOU
or GUE.  Without this patch I was barely able to get 1 Gb/s of throughput.
With this patch applied I am now at least getting around 6 Gb/s.

The issue is due to the fact that with FOU or GUE applied we do not provide
a transport offset pointing to the GRE header, nor do we offload it in
software as the GRE header is completely skipped by GSO and treated like a
VXLAN or GENEVE type header.  As such we need to prevent the stack from
generating it and also prevent GRE from generating it via any interface we
create.

Fixes: c3483384ee511 ("gro: Allow tunnel stacking in the case of FOU/GUE")
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 29 insertions, 4 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cb0d5d09c2e4..8395308a2445 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2120,7 +2120,10 @@ struct napi_gro_cb {
         /* Used in foo-over-udp, set in udp[46]_gro_receive */
         u8      is_ipv6:1;
 
-        /* 7 bit hole */
+        /* Used in GRE, set in fou/gue_gro_receive */
+        u8      is_fou:1;
+
+        /* 6 bit hole */
 
         /* used to support CHECKSUM_COMPLETE for tunneling protocols */
         __wsum  csum;
diff --git a/net/core/dev.c b/net/core/dev.c
index b9bcbe77d913..77a71cd68535 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4439,6 +4439,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
                 NAPI_GRO_CB(skb)->flush = 0;
                 NAPI_GRO_CB(skb)->free = 0;
                 NAPI_GRO_CB(skb)->encap_mark = 0;
+                NAPI_GRO_CB(skb)->is_fou = 0;
                 NAPI_GRO_CB(skb)->gro_remcsum_start = 0;
 
                 /* Setup for GRO checksum validation */
diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index 5a94aea280d3..a39068b4a4d9 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -203,6 +203,9 @@ static struct sk_buff **fou_gro_receive(struct sk_buff **head,
          */
         NAPI_GRO_CB(skb)->encap_mark = 0;
 
+        /* Flag this frame as already having an outer encap header */
+        NAPI_GRO_CB(skb)->is_fou = 1;
+
         rcu_read_lock();
         offloads = NAPI_GRO_CB(skb)->is_ipv6 ? inet6_offloads : inet_offloads;
         ops = rcu_dereference(offloads[proto]);
@@ -368,6 +371,9 @@ static struct sk_buff **gue_gro_receive(struct sk_buff **head,
          */
         NAPI_GRO_CB(skb)->encap_mark = 0;
 
+        /* Flag this frame as already having an outer encap header */
+        NAPI_GRO_CB(skb)->is_fou = 1;
+
         rcu_read_lock();
         offloads = NAPI_GRO_CB(skb)->is_ipv6 ? inet6_offloads : inet_offloads;
         ops = rcu_dereference(offloads[guehdr->proto_ctype]);
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index c47539d04b88..6a5bd4317866 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -150,6 +150,14 @@ static struct sk_buff **gre_gro_receive(struct sk_buff **head,
         if ((greh->flags & ~(GRE_KEY|GRE_CSUM)) != 0)
                 goto out;
 
+        /* We can only support GRE_CSUM if we can track the location of
+         * the GRE header.  In the case of FOU/GUE we cannot because the
+         * outer UDP header displaces the GRE header leaving us in a state
+         * of limbo.
+         */
+        if ((greh->flags & GRE_CSUM) && NAPI_GRO_CB(skb)->is_fou)
+                goto out;
+
         type = greh->protocol;
 
         rcu_read_lock();
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 31936d387cfd..af5d1f38217f 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -862,9 +862,16 @@ static void __gre_tunnel_init(struct net_device *dev)
         dev->hw_features        |= GRE_FEATURES;
 
         if (!(tunnel->parms.o_flags & TUNNEL_SEQ)) {
-                /* TCP offload with GRE SEQ is not supported. */
-                dev->features    |= NETIF_F_GSO_SOFTWARE;
-                dev->hw_features |= NETIF_F_GSO_SOFTWARE;
+                /* TCP offload with GRE SEQ is not supported, nor
+                 * can we support 2 levels of outer headers requiring
+                 * an update.
+                 */
+                if (!(tunnel->parms.o_flags & TUNNEL_CSUM) ||
+                    (tunnel->encap.type == TUNNEL_ENCAP_NONE)) {
+                        dev->features    |= NETIF_F_GSO_SOFTWARE;
+                        dev->hw_features |= NETIF_F_GSO_SOFTWARE;
+                }
+
                 /* Can use a lockless transmit, unless we generate
                  * output sequences
                  */