udp_tunnel: use static call for GRO hooks when possible

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.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/6fd1f9c7651151493ecab174e7b8386a1534170d.1741718157.git.pabeni@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/udp_tunnel.h

@@ -205,16 +205,20 @@ 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)
 {
 	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;
 

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);
 }

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);
 }