GSO: Add GSO type for fixed IPv4 ID

This patch adds support for TSO using IPv4 headers with a fixed IP ID
field. This is meant to allow us to do a lossless GRO in the case of TCP
flows that use a fixed IP ID such as those that convert IPv6 header to IPv4
headers.

In addition I am adding a feature that for now I am referring to TSO with
IP ID mangling. Basically when this flag is enabled the device has the
option to either output the flow with incrementing IP IDs or with a fixed
IP ID regardless of what the original IP ID ordering was. This is useful
in cases where the DF bit is set and we do not care if the original IP ID
value is maintained.

Signed-off-by: Alexander Duyck <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/netdev_features.h

···
 	NETIF_F_UFO_BIT,		/* ... UDPv4 fragmentation */
 	NETIF_F_GSO_ROBUST_BIT,		/* ... ->SKB_GSO_DODGY */
 	NETIF_F_TSO_ECN_BIT,		/* ... TCP ECN support */
+	NETIF_F_TSO_MANGLEID_BIT,	/* ... IPV4 ID mangling allowed */
 	NETIF_F_TSO6_BIT,		/* ... TCPv6 segmentation */
 	NETIF_F_FSO_BIT,		/* ... FCoE segmentation */
 	NETIF_F_GSO_GRE_BIT,		/* ... GRE with TSO */
···
 #define NETIF_F_GSO_SIT		__NETIF_F(GSO_SIT)
 #define NETIF_F_GSO_UDP_TUNNEL	__NETIF_F(GSO_UDP_TUNNEL)
 #define NETIF_F_GSO_UDP_TUNNEL_CSUM __NETIF_F(GSO_UDP_TUNNEL_CSUM)
+#define NETIF_F_TSO_MANGLEID	__NETIF_F(TSO_MANGLEID)
 #define NETIF_F_GSO_TUNNEL_REMCSUM __NETIF_F(GSO_TUNNEL_REMCSUM)
 #define NETIF_F_HW_VLAN_STAG_FILTER __NETIF_F(HW_VLAN_STAG_FILTER)
 #define NETIF_F_HW_VLAN_STAG_RX	__NETIF_F(HW_VLAN_STAG_RX)
···
 
 /* List of features with software fallbacks. */
 #define NETIF_F_GSO_SOFTWARE	(NETIF_F_TSO | NETIF_F_TSO_ECN | \
+				 NETIF_F_TSO_MANGLEID | \
 				 NETIF_F_TSO6 | NETIF_F_UFO)
 
 /* List of IP checksum features. Note that NETIF_F_ HW_CSUM should not be

include/linux/netdevice.h

···
 	BUILD_BUG_ON(SKB_GSO_UDP     != (NETIF_F_UFO >> NETIF_F_GSO_SHIFT));
 	BUILD_BUG_ON(SKB_GSO_DODGY   != (NETIF_F_GSO_ROBUST >> NETIF_F_GSO_SHIFT));
 	BUILD_BUG_ON(SKB_GSO_TCP_ECN != (NETIF_F_TSO_ECN >> NETIF_F_GSO_SHIFT));
+	BUILD_BUG_ON(SKB_GSO_TCP_FIXEDID != (NETIF_F_TSO_MANGLEID >> NETIF_F_GSO_SHIFT));
 	BUILD_BUG_ON(SKB_GSO_TCPV6   != (NETIF_F_TSO6 >> NETIF_F_GSO_SHIFT));
 	BUILD_BUG_ON(SKB_GSO_FCOE    != (NETIF_F_FSO >> NETIF_F_GSO_SHIFT));
 	BUILD_BUG_ON(SKB_GSO_GRE     != (NETIF_F_GSO_GRE >> NETIF_F_GSO_SHIFT));

include/linux/skbuff.h

···
 	/* This indicates the tcp segment has CWR set. */
 	SKB_GSO_TCP_ECN = 1 << 3,
 
-	SKB_GSO_TCPV6 = 1 << 4,
+	SKB_GSO_TCP_FIXEDID = 1 << 4,
 
-	SKB_GSO_FCOE = 1 << 5,
+	SKB_GSO_TCPV6 = 1 << 5,
 
-	SKB_GSO_GRE = 1 << 6,
+	SKB_GSO_FCOE = 1 << 6,
 
-	SKB_GSO_GRE_CSUM = 1 << 7,
+	SKB_GSO_GRE = 1 << 7,
 
-	SKB_GSO_IPIP = 1 << 8,
+	SKB_GSO_GRE_CSUM = 1 << 8,
 
-	SKB_GSO_SIT = 1 << 9,
+	SKB_GSO_IPIP = 1 << 9,
 
-	SKB_GSO_UDP_TUNNEL = 1 << 10,
+	SKB_GSO_SIT = 1 << 10,
 
-	SKB_GSO_UDP_TUNNEL_CSUM = 1 << 11,
+	SKB_GSO_UDP_TUNNEL = 1 << 11,
 
-	SKB_GSO_TUNNEL_REMCSUM = 1 << 12,
+	SKB_GSO_UDP_TUNNEL_CSUM = 1 << 12,
+
+	SKB_GSO_TUNNEL_REMCSUM = 1 << 13,
 };
 
 #if BITS_PER_LONG > 32

net/core/dev.c

···
 	return vlan_features_check(skb, features);
 }
 
+static netdev_features_t gso_features_check(const struct sk_buff *skb,
+					    struct net_device *dev,
+					    netdev_features_t features)
+{
+	u16 gso_segs = skb_shinfo(skb)->gso_segs;
+
+	if (gso_segs > dev->gso_max_segs)
+		return features & ~NETIF_F_GSO_MASK;
+
+	/* Make sure to clear the IPv4 ID mangling feature if
+	 * the IPv4 header has the potential to be fragmented.
+	 */
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4) {
+		struct iphdr *iph = skb->encapsulation ?
+				    inner_ip_hdr(skb) : ip_hdr(skb);
+
+		if (!(iph->frag_off & htons(IP_DF)))
+			features &= ~NETIF_F_TSO_MANGLEID;
+	}
+
+	return features;
+}
+
 netdev_features_t netif_skb_features(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
 	netdev_features_t features = dev->features;
-	u16 gso_segs = skb_shinfo(skb)->gso_segs;
 
-	if (gso_segs > dev->gso_max_segs)
-		features &= ~NETIF_F_GSO_MASK;
+	if (skb_is_gso(skb))
+		features = gso_features_check(skb, dev, features);
 
 	/* If encapsulation offload request, verify we are testing
 	 * hardware encapsulation features instead of standard
···
 	dev->features |= NETIF_F_SOFT_FEATURES;
 	dev->wanted_features = dev->features & dev->hw_features;
 
-	if (!(dev->flags & IFF_LOOPBACK)) {
+	if (!(dev->flags & IFF_LOOPBACK))
 		dev->hw_features |= NETIF_F_NOCACHE_COPY;
-	}
+
+	if (dev->hw_features & NETIF_F_TSO)
+		dev->hw_features |= NETIF_F_TSO_MANGLEID;
 
 	/* Make NETIF_F_HIGHDMA inheritable to VLAN devices.
 	 */

net/core/ethtool.c

···
 	[NETIF_F_UFO_BIT] =              "tx-udp-fragmentation",
 	[NETIF_F_GSO_ROBUST_BIT] =       "tx-gso-robust",
 	[NETIF_F_TSO_ECN_BIT] =          "tx-tcp-ecn-segmentation",
+	[NETIF_F_TSO_MANGLEID_BIT] =	 "tx-tcp-mangleid-segmentation",
 	[NETIF_F_TSO6_BIT] =             "tx-tcp6-segmentation",
 	[NETIF_F_FSO_BIT] =              "tx-fcoe-segmentation",
 	[NETIF_F_GSO_GRE_BIT] =		 "tx-gre-segmentation",

net/ipv4/af_inet.c

···
 static struct sk_buff *inet_gso_segment(struct sk_buff *skb,
 					netdev_features_t features)
 {
+	bool udpfrag = false, fixedid = false, encap;
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	const struct net_offload *ops;
 	unsigned int offset = 0;
-	bool udpfrag, encap;
 	struct iphdr *iph;
 	int proto;
 	int nhoff;
···
 		       SKB_GSO_TCPV6 |
 		       SKB_GSO_UDP_TUNNEL |
 		       SKB_GSO_UDP_TUNNEL_CSUM |
+		       SKB_GSO_TCP_FIXEDID |
 		       SKB_GSO_TUNNEL_REMCSUM |
 		       0)))
 		goto out;
···
 
 	segs = ERR_PTR(-EPROTONOSUPPORT);
 
-	if (skb->encapsulation &&
-	    skb_shinfo(skb)->gso_type & (SKB_GSO_SIT|SKB_GSO_IPIP))
-		udpfrag = proto == IPPROTO_UDP && encap;
-	else
-		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation;
+	if (!skb->encapsulation || encap) {
+		udpfrag = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
+		fixedid = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TCP_FIXEDID);
+
+		/* fixed ID is invalid if DF bit is not set */
+		if (fixedid && !(iph->frag_off & htons(IP_DF)))
+			goto out;
+	}
 
 	ops = rcu_dereference(inet_offloads[proto]);
 	if (likely(ops && ops->callbacks.gso_segment))
···
 	do {
 		iph = (struct iphdr *)(skb_mac_header(skb) + nhoff);
 		if (udpfrag) {
-			iph->id = htons(id);
 			iph->frag_off = htons(offset >> 3);
 			if (skb->next)
 				iph->frag_off |= htons(IP_MF);
 			offset += skb->len - nhoff - ihl;
-		} else {
+		} else if (!fixedid) {
 			iph->id = htons(id++);
 		}
 		iph->tot_len = htons(skb->len - nhoff);

net/ipv4/gre_offload.c

···
 				  SKB_GSO_UDP |
 				  SKB_GSO_DODGY |
 				  SKB_GSO_TCP_ECN |
+				  SKB_GSO_TCP_FIXEDID |
 				  SKB_GSO_GRE |
 				  SKB_GSO_GRE_CSUM |
 				  SKB_GSO_IPIP |

net/ipv4/tcp_offload.c

···
 			     ~(SKB_GSO_TCPV4 |
 			       SKB_GSO_DODGY |
 			       SKB_GSO_TCP_ECN |
+			       SKB_GSO_TCP_FIXEDID |
 			       SKB_GSO_TCPV6 |
 			       SKB_GSO_GRE |
 			       SKB_GSO_GRE_CSUM |
···
 			       SKB_GSO_UDP_TUNNEL_CSUM |
 			       SKB_GSO_TUNNEL_REMCSUM |
 			       0) ||
-			     !(type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))))
+			     !(type & (SKB_GSO_TCPV4 |
+				       SKB_GSO_TCPV6))))
 			goto out;
 
 		skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);

net/ipv6/ip6_offload.c

···
 		       SKB_GSO_UDP |
 		       SKB_GSO_DODGY |
 		       SKB_GSO_TCP_ECN |
+		       SKB_GSO_TCP_FIXEDID |
+		       SKB_GSO_TCPV6 |
 		       SKB_GSO_GRE |
 		       SKB_GSO_GRE_CSUM |
 		       SKB_GSO_IPIP |
···
 		       SKB_GSO_UDP_TUNNEL |
 		       SKB_GSO_UDP_TUNNEL_CSUM |
 		       SKB_GSO_TUNNEL_REMCSUM |
-		       SKB_GSO_TCPV6 |
 		       0)))
 		goto out;
 

net/mpls/mpls_gso.c

···
 				  SKB_GSO_TCPV6 |
 				  SKB_GSO_UDP |
 				  SKB_GSO_DODGY |
+				  SKB_GSO_TCP_FIXEDID |
 				  SKB_GSO_TCP_ECN)))
 		goto out;