This patch adopts the proposed RFC 6935 by allowing null UDP checksums
even if the tunnel protocol is IPv6. This is already supported by Linux
through the udp6zerocsumtx tunnel option. It is disabled by default and
IPv6 tunnels are flagged as requiring a checksum, but this patch enables
the user to set csum=false on IPv6 tunnels.

Signed-off-by: Mike Pattrick <[email protected]>
---
v2: Changed documentation, and added a NEWS item
v3: NEWS file merge conflict
v4: Better comments, new test
---
 NEWS                          |  4 ++++
 lib/netdev-native-tnl.c       |  2 +-
 lib/netdev-vport.c            | 17 +++++++++++++++--
 lib/netdev.h                  | 18 +++++++++++++++++-
 ofproto/tunnel.c              | 11 +++++++++--
 tests/tunnel-push-pop-ipv6.at |  9 +++++++++
 tests/tunnel-push-pop.at      |  7 +++++++
 tests/tunnel.at               |  2 +-
 vswitchd/vswitch.xml          | 12 +++++++++---
 9 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/NEWS b/NEWS
index c9e4064e6..6c8c4a2dc 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,10 @@ Post-v3.3.0
      * Conntrack now supports 'random' flag for selecting ports in a range
        while natting and 'persistent' flag for selection of the IP address
        from a range.
+     * IPv6 UDP tunnel encapsulation including Geneve and VXLAN will now
+       honour the csum option.  Configuring the interface with
+       "options:csum=false" now has the same effect as the udp6zerocsumtx
+       option has with Linux kernel UDP tunnels.
 
 
 v3.3.0 - 16 Feb 2024
diff --git a/lib/netdev-native-tnl.c b/lib/netdev-native-tnl.c
index dee9ab344..e8258bc4e 100644
--- a/lib/netdev-native-tnl.c
+++ b/lib/netdev-native-tnl.c
@@ -424,7 +424,7 @@ udp_build_header(const struct netdev_tunnel_config *tnl_cfg,
     udp = netdev_tnl_ip_build_header(data, params, IPPROTO_UDP, 0);
     udp->udp_dst = tnl_cfg->dst_port;
 
-    if (params->is_ipv6 || params->flow->tunnel.flags & FLOW_TNL_F_CSUM) {
+    if (params->flow->tunnel.flags & FLOW_TNL_F_CSUM) {
         /* Write a value in now to mark that we should compute the checksum
          * later. 0xffff is handy because it is transparent to the
          * calculation. */
diff --git a/lib/netdev-vport.c b/lib/netdev-vport.c
index 60caa02fb..e51542e32 100644
--- a/lib/netdev-vport.c
+++ b/lib/netdev-vport.c
@@ -702,7 +702,9 @@ set_tunnel_config(struct netdev *dev_, const struct smap 
*args, char **errp)
             tnl_cfg.dst_port = htons(atoi(node->value));
         } else if (!strcmp(node->key, "csum") && has_csum) {
             if (!strcmp(node->value, "true")) {
-                tnl_cfg.csum = true;
+                tnl_cfg.csum = NETDEV_TNL_CSUM_ENABLED;
+            } else if (!strcmp(node->value, "false")) {
+                tnl_cfg.csum = NETDEV_TNL_CSUM_DISABLED;
             }
         } else if (!strcmp(node->key, "seq") && has_seq) {
             if (!strcmp(node->value, "true")) {
@@ -850,6 +852,15 @@ set_tunnel_config(struct netdev *dev_, const struct smap 
*args, char **errp)
         }
     }
 
+    /* The default csum state for GRE is special as it does have an optional
+     * checksum but the default configuration isn't correlated with IP version
+     * like UDP tunnels are.  Likewise, tunnels with checksum at all must be in
+     * this state. */
+    if (tnl_cfg.csum == NETDEV_TNL_CSUM_DEFAULT &&
+        (!has_csum || strstr(type, "gre"))) {
+        tnl_cfg.csum = NETDEV_TNL_DEFAULT_NO_CSUM;
+    }
+
     enum tunnel_layers layers = tunnel_supported_layers(type, &tnl_cfg);
     const char *full_type = (strcmp(type, "vxlan") ? type
                              : (tnl_cfg.exts & (1 << OVS_VXLAN_EXT_GPE)
@@ -1026,8 +1037,10 @@ get_tunnel_config(const struct netdev *dev, struct smap 
*args)
         }
     }
 
-    if (tnl_cfg->csum) {
+    if (tnl_cfg->csum == NETDEV_TNL_CSUM_ENABLED) {
         smap_add(args, "csum", "true");
+    } else if (tnl_cfg->csum == NETDEV_TNL_CSUM_DISABLED) {
+        smap_add(args, "csum", "false");
     }
 
     if (tnl_cfg->set_seq) {
diff --git a/lib/netdev.h b/lib/netdev.h
index 67a8486bd..5d253157c 100644
--- a/lib/netdev.h
+++ b/lib/netdev.h
@@ -111,6 +111,22 @@ enum netdev_srv6_flowlabel {
     SRV6_FLOWLABEL_COMPUTE,
 };
 
+enum netdev_tnl_csum {
+    /* Default value for UDP tunnels if no configurations is present.  Enforce
+     * checksum calculation in IPv6 tunnels, disable in IPv4 tunnels. */
+    NETDEV_TNL_CSUM_DEFAULT = 0,
+
+    /* Checksum explicitly to be calculated. */
+    NETDEV_TNL_CSUM_ENABLED,
+
+    /* Checksum calculation explicitly disabled. */
+    NETDEV_TNL_CSUM_DISABLED,
+
+    /* A value for when there is no checksum or the default value is no
+     * checksum reguardless of IP version. */
+    NETDEV_TNL_DEFAULT_NO_CSUM,
+};
+
 /* Configuration specific to tunnels. */
 struct netdev_tunnel_config {
     ovs_be64 in_key;
@@ -139,7 +155,7 @@ struct netdev_tunnel_config {
     uint8_t tos;
     bool tos_inherit;
 
-    bool csum;
+    enum netdev_tnl_csum csum;
     bool dont_fragment;
     enum netdev_pt_mode pt_mode;
 
diff --git a/ofproto/tunnel.c b/ofproto/tunnel.c
index 80ddee78a..6f462874e 100644
--- a/ofproto/tunnel.c
+++ b/ofproto/tunnel.c
@@ -465,9 +465,14 @@ tnl_port_send(const struct ofport_dpif *ofport, struct 
flow *flow,
 
     flow->tunnel.flags &= ~(FLOW_TNL_F_MASK & ~FLOW_TNL_PUB_F_MASK);
     flow->tunnel.flags |= (cfg->dont_fragment ? FLOW_TNL_F_DONT_FRAGMENT : 0)
-        | (cfg->csum ? FLOW_TNL_F_CSUM : 0)
         | (cfg->out_key_present ? FLOW_TNL_F_KEY : 0);
 
+    if (cfg->csum == NETDEV_TNL_CSUM_ENABLED) {
+        flow->tunnel.flags |= FLOW_TNL_F_CSUM;
+    } else if (cfg->csum == NETDEV_TNL_CSUM_DEFAULT && !flow->tunnel.ip_dst) {
+        flow->tunnel.flags |= FLOW_TNL_F_CSUM;
+    }
+
     if (cfg->set_egress_pkt_mark) {
         flow->pkt_mark = cfg->egress_pkt_mark;
         wc->masks.pkt_mark = UINT32_MAX;
@@ -706,8 +711,10 @@ tnl_port_format(const struct tnl_port *tnl_port, struct ds 
*ds)
         ds_put_cstr(ds, ", df=false");
     }
 
-    if (cfg->csum) {
+    if (cfg->csum == NETDEV_TNL_CSUM_ENABLED) {
         ds_put_cstr(ds, ", csum=true");
+    } else if (cfg->csum == NETDEV_TNL_CSUM_DISABLED) {
+        ds_put_cstr(ds, ", csum=false");
     }
 
     ds_put_cstr(ds, ")\n");
diff --git a/tests/tunnel-push-pop-ipv6.at b/tests/tunnel-push-pop-ipv6.at
index 3f2cf8429..394bdc81c 100644
--- a/tests/tunnel-push-pop-ipv6.at
+++ b/tests/tunnel-push-pop-ipv6.at
@@ -610,6 +610,15 @@ AT_CHECK([ovs-appctl tnl/arp/show | tail -n+3 | sort], 
[0], [dnl
 2001:cafe::93                                 f8:bc:12:44:34:b7   br0
 ])
 
+dnl Disable checksum from VXLAN port.
+AT_CHECK([ovs-vsctl set Interface t3 options:csum=false])
+AT_CHECK([ovs-ofctl del-flows int-br])
+AT_CHECK([ovs-ofctl add-flow int-br action=4])
+AT_CHECK([ovs-appctl ofproto/trace ovs-dummy 
'in_port(2),eth(src=36:b1:ee:7c:01:01,dst=36:b1:ee:7c:01:02),eth_type(0x0800),ipv4(src=1.1.3.88,dst=1.1.3.112,proto=47,tos=0,ttl=64,frag=no)'],
 [0], [stdout])
+AT_CHECK([tail -1 stdout], [0],
+  [Datapath actions: 
tnl_push(tnl_port(4789),header(size=70,type=4,eth(dst=f8:bc:12:44:34:b7,src=aa:55:aa:55:00:00,dl_type=0x86dd),ipv6(src=2001:cafe::88,dst=2001:cafe::93,label=0,proto=17,tclass=0x0,hlimit=64),udp(src=0,dst=4789,csum=0x0),vxlan(flags=0x8000000,vni=0x0)),out_port(100)),1
+])
+
 ovs-appctl time/warp 10000
 
 AT_CHECK([ovs-vsctl del-port int-br t3 \
diff --git a/tests/tunnel-push-pop.at b/tests/tunnel-push-pop.at
index 97405636f..d571e60c5 100644
--- a/tests/tunnel-push-pop.at
+++ b/tests/tunnel-push-pop.at
@@ -642,6 +642,13 @@ AT_CHECK([tail -1 stdout], [0],
   [Datapath actions: 
tnl_push(tnl_port(4789),header(size=50,type=4,eth(dst=f8:bc:12:44:34:b6,src=aa:55:aa:55:00:00,dl_type=0x0800),ipv4(src=1.1.2.88,dst=1.1.2.92,proto=17,tos=0,ttl=64,frag=0x4000),udp(src=0,dst=4789,csum=0x0),vxlan(flags=0x8000000,vni=0x7b)),out_port(100)),1
 ])
 
+dnl Check VXLAN tunnel push with checksum.
+AT_CHECK([ovs-vsctl set Interface t2 options:csum=true])
+AT_CHECK([ovs-appctl ofproto/trace ovs-dummy 
'in_port(2),eth(src=36:b1:ee:7c:01:01,dst=36:b1:ee:7c:01:02),eth_type(0x0800),ipv4(src=1.1.3.88,dst=1.1.3.112,proto=47,tos=0,ttl=64,frag=no)'],
 [0], [stdout])
+AT_CHECK([tail -1 stdout], [0],
+  [Datapath actions: 
tnl_push(tnl_port(4789),header(size=50,type=4,eth(dst=f8:bc:12:44:34:b6,src=aa:55:aa:55:00:00,dl_type=0x0800),ipv4(src=1.1.2.88,dst=1.1.2.92,proto=17,tos=0,ttl=64,frag=0x4000),udp(src=0,dst=4789,csum=0xffff),vxlan(flags=0x8000000,vni=0x7b)),out_port(100)),1
+])
+
 AT_CHECK([ovs-appctl tnl/neigh/show | tail -n+3 | sort], [0], [dnl
 1.1.2.92                                      f8:bc:12:44:34:b6   br0
 1.1.2.93                                      f8:bc:12:44:34:b7   br0
diff --git a/tests/tunnel.at b/tests/tunnel.at
index 9d539ee6f..31e935901 100644
--- a/tests/tunnel.at
+++ b/tests/tunnel.at
@@ -1038,7 +1038,7 @@ AT_CHECK([ovs-ofctl add-flows br0 flows.txt])
 
 AT_CHECK([ovs-appctl ofproto/trace ovs-dummy 
'tunnel(tun_id=0,src=1.1.1.1,dst=1.1.1.2,ttl=64),in_port(4789)'], [0], [stdout])
 AT_CHECK([tail -1 stdout], [0],
-  [Datapath actions: 
set(tunnel(ipv6_dst=2001:cafe::1,ttl=64,tp_dst=4789,flags(df))),4789
+  [Datapath actions: 
set(tunnel(ipv6_dst=2001:cafe::1,ttl=64,tp_dst=4789,flags(df|csum))),4789
 ])
 
 AT_CHECK([ovs-appctl ofproto/trace ovs-dummy 
'tunnel(tun_id=0x0,ipv6_src=2001:cafe::1,ipv6_dst=2001:cafe::2,ttl=64),in_port(4789)'],
 [0], [stdout])
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index 8a1b607d7..5c3aa2a2a 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -3207,9 +3207,15 @@
         <column name="options" key="csum" type='{"type": "boolean"}'>
           <p>
             Optional.  Compute encapsulation header (either GRE or UDP)
-            checksums on outgoing packets.  Default is disabled, set to
-            <code>true</code> to enable.  Checksums present on incoming
-            packets will be validated regardless of this setting.
+            checksums on outgoing packets.  When unset (the default value),
+            checksum computing for outgoing packets is enabled for UDP IPv6
+            tunnels, and disabled for IPv4 UDP and GRE tunnels.  When set to
+            <code>false</code>, no checksums will be computed for outgoing
+            tunnel encapsulation headers.  When <code>true</code>, checksums
+            will be computed for all outgoing tunnel encapsulation headers.
+            Checksums present on incoming packets will be validated
+            regardless of this setting.  Incoming packets without a checksum
+            will also be accepted regardless of this setting.
           </p>
 
           <p>
-- 
2.39.3

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