[PATCH v4 net-next 2/2] udp_tunnel: use static call for GRO hooks when possible

Paolo Abeni
2025-03-11T20:42:53Z

It's quite common to have a single UDP tunnel type active in the
whole system. In such a case we can replace the indirect call for
the UDP tunnel GRO callback with a static call.

Add the related accounting in the control path and switch to static
call when possible. To keep the code simple use a static array for
the registered tunnel types, and size such array based on the kernel
config.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v3 -> v4:
- fix CONFIG_FOE typo
- avoid gaps in gro types array
- drop WARN_ON in dummy_gro_rcv()

v2 -> v3:
- avoid unneeded checks in udp_tunnel_update_gro_rcv()

v1 -> v2:
- fix UDP_TUNNEL=n build
---
include/net/udp_tunnel.h | 4 ++
net/ipv4/udp_offload.c | 130 ++++++++++++++++++++++++++++++++++++-
net/ipv4/udp_tunnel_core.c | 2 +
3 files changed, 135 insertions(+), 1 deletion(-)

diff --git a/include/net/udp_tunnel.h b/include/net/udp_tunnel.h
index eda0f3e2f65fa..a7b230867eb14 100644
--- a/include/net/udp_tunnel.h
+++ b/include/net/udp_tunnel.h
@@ -205,9 +205,11 @@ static inline void udp_tunnel_encap_enable(struct sock *sk)

#if IS_ENABLED(CONFIG_NET_UDP_TUNNEL)
void udp_tunnel_update_gro_lookup(struct net *net, struct sock *sk, bool add);
+void udp_tunnel_update_gro_rcv(struct sock *sk, bool add);
#else
static inline void udp_tunnel_update_gro_lookup(struct net *net,
struct sock *sk, bool add) {}
+static inline void udp_tunnel_update_gro_rcv(struct sock *sk, bool add) {}
#endif

static inline void udp_tunnel_cleanup_gro(struct sock *sk)
@@ -215,6 +217,8 @@ static inline void udp_tunnel_cleanup_gro(struct sock *sk)
struct udp_sock *up = udp_sk(sk);
struct net *net = sock_net(sk);

+ udp_tunnel_update_gro_rcv(sk, false);
+
if (!up->tunnel_list.pprev)
return;

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index e36d8a234848f..088aa8cb8ac0c 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -15,6 +15,37 @@
#include <net/udp_tunnel.h>

#if IS_ENABLED(CONFIG_NET_UDP_TUNNEL)
+
+/*
+ * Dummy GRO tunnel callback, exists mainly to avoid dangling/NULL
+ * values for the udp tunnel static call.
+ */
+static struct sk_buff *dummy_gro_rcv(struct sock *sk,
+ struct list_head *head,
+ struct sk_buff *skb)
+{
+ NAPI_GRO_CB(skb)->flush = 1;
+ return NULL;
+}
+
+typedef struct sk_buff *(*udp_tunnel_gro_rcv_t)(struct sock *sk,
+ struct list_head *head,
+ struct sk_buff *skb);
+
+struct udp_tunnel_type_entry {
+ udp_tunnel_gro_rcv_t gro_receive;
+ refcount_t count;
+};
+
+#define UDP_MAX_TUNNEL_TYPES (IS_ENABLED(CONFIG_GENEVE) + \
+ IS_ENABLED(CONFIG_VXLAN) * 2 + \
+ IS_ENABLED(CONFIG_NET_FOU) * 2)
+
+DEFINE_STATIC_CALL(udp_tunnel_gro_rcv, dummy_gro_rcv);
+static DEFINE_STATIC_KEY_FALSE(udp_tunnel_static_call);
+static struct mutex udp_tunnel_gro_type_lock;
+static struct udp_tunnel_type_entry udp_tunnel_gro_types[UDP_MAX_TUNNEL_TYPES];
+static unsigned int udp_tunnel_gro_type_nr;
static DEFINE_SPINLOCK(udp_tunnel_gro_lock);

void udp_tunnel_update_gro_lookup(struct net *net, struct sock *sk, bool add)
@@ -43,6 +74,101 @@ void udp_tunnel_update_gro_lookup(struct net *net, struct sock *sk, bool add)
spin_unlock(&udp_tunnel_gro_lock);
}
EXPORT_SYMBOL_GPL(udp_tunnel_update_gro_lookup);
+
+void udp_tunnel_update_gro_rcv(struct sock *sk, bool add)
+{
+ struct udp_tunnel_type_entry *cur = NULL;
+ struct udp_sock *up = udp_sk(sk);
+ int i, old_gro_type_nr;
+
+ if (!up->gro_receive)
+ return;
+
+ mutex_lock(&udp_tunnel_gro_type_lock);
+ for (i = 0; i < udp_tunnel_gro_type_nr; i++)
+ if (udp_tunnel_gro_types[i].gro_receive == up->gro_receive)
+ cur = &udp_tunnel_gro_types[i];
+
+ old_gro_type_nr = udp_tunnel_gro_type_nr;
+ if (add) {
+ /*
+ * Update the matching entry, if found, or add a new one
+ * if needed
+ */
+ if (cur) {
+ refcount_inc(&cur->count);
+ goto out;
+ }
+
+ if (unlikely(udp_tunnel_gro_type_nr == UDP_MAX_TUNNEL_TYPES)) {
+ pr_err_once("Too many UDP tunnel types, please increase UDP_MAX_TUNNEL_TYPES\n");
+ /* Ensure static call will never be enabled */
+ udp_tunnel_gro_type_nr = UDP_MAX_TUNNEL_TYPES + 2;
+ goto out;
+ }
+
+ cur = &udp_tunnel_gro_types[udp_tunnel_gro_type_nr++];
+ refcount_set(&cur->count, 1);
+ cur->gro_receive = up->gro_receive;
+ } else {
+ /*
+ * The stack cleanups only successfully added tunnel, the
+ * lookup on removal should never fail.
+ */
+ if (WARN_ON_ONCE(!cur))
+ goto out;
+
+ if (!refcount_dec_and_test(&cur->count))
+ goto out;
+
+ /* avoid gaps, so that the enable tunnel has always id 0 */
+ *cur = udp_tunnel_gro_types[--udp_tunnel_gro_type_nr];
+ }
+
+ if (udp_tunnel_gro_type_nr == 1) {
+ static_call_update(udp_tunnel_gro_rcv,
+ udp_tunnel_gro_types[0].gro_receive);
+ static_branch_enable(&udp_tunnel_static_call);
+ } else if (old_gro_type_nr == 1) {
+ static_branch_disable(&udp_tunnel_static_call);
+ static_call_update(udp_tunnel_gro_rcv, dummy_gro_rcv);
+ }
+
+out:
+ mutex_unlock(&udp_tunnel_gro_type_lock);
+}
+EXPORT_SYMBOL_GPL(udp_tunnel_update_gro_rcv);
+
+static void udp_tunnel_gro_init(void)
+{
+ mutex_init(&udp_tunnel_gro_type_lock);
+}
+
+static struct sk_buff *udp_tunnel_gro_rcv(struct sock *sk,
+ struct list_head *head,
+ struct sk_buff *skb)
+{
+ if (static_branch_likely(&udp_tunnel_static_call)) {
+ if (unlikely(gro_recursion_inc_test(skb))) {
+ NAPI_GRO_CB(skb)->flush |= 1;
+ return NULL;
+ }
+ return static_call(udp_tunnel_gro_rcv)(sk, head, skb);
+ }
+ return call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);
+}
+
+#else
+
+static void udp_tunnel_gro_init(void) {}
+
+static struct sk_buff *udp_tunnel_gro_rcv(struct sock *sk,
+ struct list_head *head,
+ struct sk_buff *skb)
+{
+ return call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);
+}
+
#endif

static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
@@ -654,7 +780,7 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,

skb_gro_pull(skb, sizeof(struct udphdr)); /* pull encapsulating udp header */
skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
- pp = call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);
+ pp = udp_tunnel_gro_rcv(sk, head, skb);

out:
skb_gro_flush_final(skb, pp, flush);
@@ -804,5 +930,7 @@ int __init udpv4_offload_init(void)
.gro_complete = udp4_gro_complete,
},
};
+
+ udp_tunnel_gro_init();
return inet_add_offload(&net_hotdata.udpv4_offload, IPPROTO_UDP);
}
diff --git a/net/ipv4/udp_tunnel_core.c b/net/ipv4/udp_tunnel_core.c
index b5695826e57ad..c49fceea83139 100644
--- a/net/ipv4/udp_tunnel_core.c
+++ b/net/ipv4/udp_tunnel_core.c
@@ -90,6 +90,8 @@ void setup_udp_tunnel_sock(struct net *net, struct socket *sock,

udp_tunnel_encap_enable(sk);

+ udp_tunnel_update_gro_rcv(sock->sk, true);
+
if (!sk->sk_dport && !sk->sk_bound_dev_if && sk_saddr_any(sock->sk))
udp_tunnel_update_gro_lookup(net, sock->sk, true);
}
--
2.48.1