udp: implement GRO for plain UDP sockets.

This is the RX counterpart of commit bec1f6f697 ("udp: generate gso
with UDP_SEGMENT"). When UDP_GRO is enabled, such socket is also
eligible for GRO in the rx path: UDP segments directed to such socket
are assembled into a larger GSO_UDP_L4 packet.

The core UDP GRO support is enabled with setsockopt(UDP_GRO).

Initial benchmark numbers:

Before:
udp rx:   1079 MB/s   769065 calls/s

After:
udp rx:   1466 MB/s    24877 calls/s

This change introduces a side effect in respect to UDP tunnels:
after a UDP tunnel creation, now the kernel performs a lookup per ingress
UDP packet, while before such lookup happened only if the ingress packet
carried a valid internal header csum.

rfc v2 -> rfc v3:
 - fixed typos in macro name and comments
 - really enforce UDP_GRO_CNT_MAX, instead of UDP_GRO_CNT_MAX + 1
 - acquire socket lock in UDP_GRO setsockopt

rfc v1 -> rfc v2:
 - use a new option to enable UDP GRO
 - use static keys to protect the UDP GRO socket lookup

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/udp.h

@@ -50,11 +50,12 @@ struct udp_sock {
 	__u8		 encap_type;	/* Is this an Encapsulation socket? */
 	unsigned char	 no_check6_tx:1,/* Send zero UDP6 checksums on TX? */
 			 no_check6_rx:1,/* Allow zero UDP6 checksums on RX? */
-			 encap_enabled:1; /* This socket enabled encap
+			 encap_enabled:1, /* This socket enabled encap
 					   * processing; UDP tunnels and
 					   * different encapsulation layer set
 					   * this
 					   */
+			 gro_enabled:1;	/* Can accept GRO packets */
 	/*
 	 * Following member retains the information to create a UDP header
 	 * when the socket is uncorked.

include/uapi/linux/udp.h

@@ -33,6 +33,7 @@ struct udphdr {
 #define UDP_NO_CHECK6_TX 101	/* Disable sending checksum for UDP6X */
 #define UDP_NO_CHECK6_RX 102	/* Disable accpeting checksum for UDP6 */
 #define UDP_SEGMENT	103	/* Set GSO segmentation size */
+#define UDP_GRO		104	/* This socket can receive UDP GRO packets */
 
 /* UDP encapsulation types */
 #define UDP_ENCAP_ESPINUDP_NON_IKE	1 /* draft-ietf-ipsec-nat-t-ike-00/01 */

net/ipv4/udp.c

@@ -2473,6 +2473,14 @@ int udp_lib_setsockopt(struct sock *sk, int level, int optname,
 		up->gso_size = val;
 		break;
 
+	case UDP_GRO:
+		lock_sock(sk);
+		if (valbool)
+			udp_tunnel_encap_enable(sk->sk_socket);
+		up->gro_enabled = valbool;
+		release_sock(sk);
+		break;
+
 	/*
 	 * 	UDP-Lite's partial checksum coverage (RFC 3828).
 	 */

net/ipv4/udp_offload.c

@@ -343,6 +343,54 @@ out:
 	return segs;
 }
 
+#define UDP_GRO_CNT_MAX 64
+static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
+					       struct sk_buff *skb)
+{
+	struct udphdr *uh = udp_hdr(skb);
+	struct sk_buff *pp = NULL;
+	struct udphdr *uh2;
+	struct sk_buff *p;
+
+	/* requires non zero csum, for symmetry with GSO */
+	if (!uh->check) {
+		NAPI_GRO_CB(skb)->flush = 1;
+		return NULL;
+	}
+
+	/* pull encapsulating udp header */
+	skb_gro_pull(skb, sizeof(struct udphdr));
+	skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
+
+	list_for_each_entry(p, head, list) {
+		if (!NAPI_GRO_CB(p)->same_flow)
+			continue;
+
+		uh2 = udp_hdr(p);
+
+		/* Match ports only, as csum is always non zero */
+		if ((*(u32 *)&uh->source != *(u32 *)&uh2->source)) {
+			NAPI_GRO_CB(p)->same_flow = 0;
+			continue;
+		}
+
+		/* Terminate the flow on len mismatch or if it grow "too much".
+		 * Under small packet flood GRO count could elsewhere grow a lot
+		 * leading to execessive truesize values
+		 */
+		if (!skb_gro_receive(p, skb) &&
+		    NAPI_GRO_CB(p)->count >= UDP_GRO_CNT_MAX)
+			pp = p;
+		else if (uh->len != uh2->len)
+			pp = p;
+
+		return pp;
+	}
+
+	/* mismatch, but we never need to flush */
+	return NULL;
+}
+
 struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
 				struct udphdr *uh, udp_lookup_t lookup)
 {
@@ -353,23 +401,27 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
 	int flush = 1;
 	struct sock *sk;
 
+	rcu_read_lock();
+	sk = (*lookup)(skb, uh->source, uh->dest);
+	if (!sk)
+		goto out_unlock;
+
+	if (udp_sk(sk)->gro_enabled) {
+		pp = call_gro_receive(udp_gro_receive_segment, head, skb);
+		rcu_read_unlock();
+		return pp;
+	}
+
 	if (NAPI_GRO_CB(skb)->encap_mark ||
 	    (skb->ip_summed != CHECKSUM_PARTIAL &&
 	     NAPI_GRO_CB(skb)->csum_cnt == 0 &&
-	     !NAPI_GRO_CB(skb)->csum_valid))
-		goto out;
+	     !NAPI_GRO_CB(skb)->csum_valid) ||
+	    !udp_sk(sk)->gro_receive)
+		goto out_unlock;
 
 	/* mark that this skb passed once through the tunnel gro layer */
 	NAPI_GRO_CB(skb)->encap_mark = 1;
 
-	rcu_read_lock();
-	sk = (*lookup)(skb, uh->source, uh->dest);
-
-	if (sk && udp_sk(sk)->gro_receive)
-		goto unflush;
-	goto out_unlock;
-
-unflush:
 	flush = 0;
 
 	list_for_each_entry(p, head, list) {
@@ -394,7 +446,6 @@ unflush:
 
 out_unlock:
 	rcu_read_unlock();
-out:
 	skb_gro_flush_final(skb, pp, flush);
 	return pp;
 }
@@ -427,6 +478,19 @@ flush:
 	return NULL;
 }
 
+static int udp_gro_complete_segment(struct sk_buff *skb)
+{
+	struct udphdr *uh = udp_hdr(skb);
+
+	skb->csum_start = (unsigned char *)uh - skb->head;
+	skb->csum_offset = offsetof(struct udphdr, check);
+	skb->ip_summed = CHECKSUM_PARTIAL;
+
+	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
+	skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_L4;
+	return 0;
+}
+
 int udp_gro_complete(struct sk_buff *skb, int nhoff,
 		     udp_lookup_t lookup)
 {
@@ -437,16 +501,21 @@ int udp_gro_complete(struct sk_buff *skb, int nhoff,
 
 	uh->len = newlen;
 
-	/* Set encapsulation before calling into inner gro_complete() functions
-	 * to make them set up the inner offsets.
-	 */
-	skb->encapsulation = 1;
-
 	rcu_read_lock();
 	sk = (*lookup)(skb, uh->source, uh->dest);
-	if (sk && udp_sk(sk)->gro_complete)
+	if (sk && udp_sk(sk)->gro_enabled) {
+		err = udp_gro_complete_segment(skb);
+	} else if (sk && udp_sk(sk)->gro_complete) {
+		skb_shinfo(skb)->gso_type = uh->check ? SKB_GSO_UDP_TUNNEL_CSUM
+					: SKB_GSO_UDP_TUNNEL;
+
+		/* Set encapsulation before calling into inner gro_complete()
+		 * functions to make them set up the inner offsets.
+		 */
+		skb->encapsulation = 1;
 		err = udp_sk(sk)->gro_complete(sk, skb,
 				nhoff + sizeof(struct udphdr));
+	}
 	rcu_read_unlock();
 
 	if (skb->remcsum_offload)
@@ -461,13 +530,9 @@ static int udp4_gro_complete(struct sk_buff *skb, int nhoff)
 	const struct iphdr *iph = ip_hdr(skb);
 	struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
 
-	if (uh->check) {
-		skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_TUNNEL_CSUM;
+	if (uh->check)
 		uh->check = ~udp_v4_check(skb->len - nhoff, iph->saddr,
 					  iph->daddr, 0);
-	} else {
-		skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_TUNNEL;
-	}
 
 	return udp_gro_complete(skb, nhoff, udp4_lib_lookup_skb);
 }

net/ipv6/udp_offload.c

@@ -147,13 +147,9 @@ static int udp6_gro_complete(struct sk_buff *skb, int nhoff)
 	const struct ipv6hdr *ipv6h = ipv6_hdr(skb);
 	struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
 
-	if (uh->check) {
-		skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_TUNNEL_CSUM;
+	if (uh->check)
 		uh->check = ~udp_v6_check(skb->len - nhoff, &ipv6h->saddr,
 					  &ipv6h->daddr, 0);
-	} else {
-		skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_TUNNEL;
-	}
 
 	return udp_gro_complete(skb, nhoff, udp6_lib_lookup_skb);
 }