[RFC PATCH net-next v6 1/2] net: pppoe: implement GRO/GSO support

Qingfang Deng
2026-03-26T08:11:34Z

From: Felix Fietkau <nbd@nbd.name>

Only handles packets where the pppoe header length field matches the exact
packet length. Significantly improves rx throughput.

When running NAT traffic through a MediaTek MT7621 devices from a host
behind PPPoE to a host directly connected via ethernet, the TCP throughput
that the device is able to handle improves from ~130 Mbit/s to ~630 Mbit/s,
using fraglist GRO.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
---
v6:
- avoid phdr->length field overflow
- restore skb_is_gso() check
- do not register GRO if INET=n
- do not check for PPP_IPV6 if IPV6=n
- tail call gro_complete
https://lore.kernel.org/netdev/20260305013852.3769-1-dqfext@gmail.com/

---
drivers/net/ppp/pppoe.c | 166 +++++++++++++++++++++++++++++++++++++++-
net/ipv4/af_inet.c | 2 +
net/ipv6/ip6_offload.c | 2 +
3 files changed, 169 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
index 1ac61c273b28..7522a8ce52fc 100644
--- a/drivers/net/ppp/pppoe.c
+++ b/drivers/net/ppp/pppoe.c
@@ -77,6 +77,7 @@
#include <net/net_namespace.h>
#include <net/netns/generic.h>
#include <net/sock.h>
+#include <net/gro.h>

#include <linux/uaccess.h>

@@ -403,7 +404,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev,
if (skb->len < len)
goto drop;

- if (pskb_trim_rcsum(skb, len))
+ if (!skb_is_gso(skb) && pskb_trim_rcsum(skb, len))
goto drop;

ph = pppoe_hdr(skb);
@@ -1097,6 +1098,165 @@ static struct pernet_operations pppoe_net_ops = {
.size = sizeof(struct pppoe_net),
};

+static u16
+compare_pppoe_header(const struct pppoe_hdr *phdr,
+ const struct pppoe_hdr *phdr2)
+{
+ __be16 proto = *(const __be16 *)(phdr + 1);
+ __be16 proto2 = *(const __be16 *)(phdr2 + 1);
+
+ return (__force u16)((phdr->sid ^ phdr2->sid) | (proto ^ proto2));
+}
+
+static __be16 pppoe_hdr_proto(const struct pppoe_hdr *phdr)
+{
+ __be16 proto = *(const __be16 *)(phdr + 1);
+
+ switch (proto) {
+ case cpu_to_be16(PPP_IP):
+ return cpu_to_be16(ETH_P_IP);
+#if IS_ENABLED(CONFIG_IPV6)
+ case cpu_to_be16(PPP_IPV6):
+ return cpu_to_be16(ETH_P_IPV6);
+#endif
+ default:
+ return 0;
+ }
+}
+
+static struct sk_buff *pppoe_gro_receive(struct list_head *head,
+ struct sk_buff *skb)
+{
+ const struct packet_offload *ptype;
+ unsigned int hlen, off_pppoe;
+ const struct pppoe_hdr *phdr;
+ struct sk_buff *pp = NULL;
+ struct sk_buff *p;
+ int flush = 1;
+ __be16 type;
+
+ off_pppoe = skb_gro_offset(skb);
+ hlen = off_pppoe + PPPOE_SES_HLEN;
+ phdr = skb_gro_header(skb, hlen, off_pppoe);
+ if (unlikely(!phdr))
+ goto out;
+
+ /* filter for session packets (type:1, ver:1, code:0) */
+ if (*(const __be16 *)phdr != cpu_to_be16(0x1100))
+ goto out;
+
+ /* ignore packets with padding or invalid length */
+ if (skb_gro_len(skb) != be16_to_cpu(phdr->length) + sizeof(*phdr))
+ goto out;
+
+ type = pppoe_hdr_proto(phdr);
+ ptype = gro_find_receive_by_type(type);
+ if (!ptype)
+ goto out;
+
+ flush = 0;
+
+ list_for_each_entry(p, head, list) {
+ const struct pppoe_hdr *phdr2;
+
+ if (!NAPI_GRO_CB(p)->same_flow)
+ continue;
+
+ phdr2 = (const struct pppoe_hdr *)(p->data + off_pppoe);
+ if (compare_pppoe_header(phdr, phdr2))
+ NAPI_GRO_CB(p)->same_flow = 0;
+ }
+
+ skb_gro_pull(skb, PPPOE_SES_HLEN);
+ skb_gro_postpull_rcsum(skb, phdr, PPPOE_SES_HLEN);
+
+ pp = indirect_call_gro_receive_inet(ptype->callbacks.gro_receive,
+ ipv6_gro_receive, inet_gro_receive,
+ head, skb);
+
+out:
+ skb_gro_flush_final(skb, pp, flush);
+
+ return pp;
+}
+
+static int pppoe_gro_complete(struct sk_buff *skb, int nhoff)
+{
+ struct pppoe_hdr *phdr = (struct pppoe_hdr *)(skb->data + nhoff);
+ __be16 type = pppoe_hdr_proto(phdr);
+ struct packet_offload *ptype;
+ unsigned int len;
+
+ ptype = gro_find_complete_by_type(type);
+ if (!ptype)
+ return -ENOENT;
+
+ len = skb->len - (nhoff + sizeof(*phdr));
+ len = min(len, 0xFFFFU);
+ phdr->length = cpu_to_be16(len);
+
+ return INDIRECT_CALL_INET(ptype->callbacks.gro_complete,
+ ipv6_gro_complete, inet_gro_complete,
+ skb, nhoff + PPPOE_SES_HLEN);
+}
+
+static struct sk_buff *pppoe_gso_segment(struct sk_buff *skb,
+ netdev_features_t features)
+{
+ unsigned int pppoe_hlen = sizeof(struct pppoe_hdr) + 2;
+ struct sk_buff *segs = ERR_PTR(-EINVAL);
+ u16 mac_offset = skb->mac_header;
+ struct packet_offload *ptype;
+ u16 mac_len = skb->mac_len;
+ struct pppoe_hdr *phdr;
+ __be16 orig_type, type;
+ int len, nhoff;
+
+ skb_reset_network_header(skb);
+ nhoff = skb_network_header(skb) - skb_mac_header(skb);
+
+ if (unlikely(!pskb_may_pull(skb, pppoe_hlen)))
+ goto out;
+
+ phdr = (struct pppoe_hdr *)skb_network_header(skb);
+ type = pppoe_hdr_proto(phdr);
+ ptype = gro_find_complete_by_type(type);
+ if (!ptype)
+ goto out;
+
+ orig_type = skb->protocol;
+ __skb_pull(skb, pppoe_hlen);
+ segs = ptype->callbacks.gso_segment(skb, features);
+ if (IS_ERR_OR_NULL(segs)) {
+ skb_gso_error_unwind(skb, orig_type, pppoe_hlen, mac_offset,
+ mac_len);
+ goto out;
+ }
+
+ skb = segs;
+ do {
+ phdr = (struct pppoe_hdr *)(skb_mac_header(skb) + nhoff);
+ len = skb->len - (nhoff + sizeof(*phdr));
+ phdr->length = cpu_to_be16(len);
+ skb->network_header = (u8 *)phdr - skb->head;
+ skb->protocol = orig_type;
+ skb_reset_mac_len(skb);
+ } while ((skb = skb->next));
+
+out:
+ return segs;
+}
+
+static struct packet_offload pppoe_packet_offload __read_mostly = {
+ .type = cpu_to_be16(ETH_P_PPP_SES),
+ .priority = 20,
+ .callbacks = {
+ .gro_receive = pppoe_gro_receive,
+ .gro_complete = pppoe_gro_complete,
+ .gso_segment = pppoe_gso_segment,
+ },
+};
+
static int __init pppoe_init(void)
{
int err;
@@ -1113,6 +1273,8 @@ static int __init pppoe_init(void)
if (err)
goto out_unregister_pppoe_proto;

+ if (IS_ENABLED(CONFIG_INET))
+ dev_add_offload(&pppoe_packet_offload);
dev_add_pack(&pppoes_ptype);
dev_add_pack(&pppoed_ptype);
register_netdevice_notifier(&pppoe_notifier);
@@ -1132,6 +1294,8 @@ static void __exit pppoe_exit(void)
unregister_netdevice_notifier(&pppoe_notifier);
dev_remove_pack(&pppoed_ptype);
dev_remove_pack(&pppoes_ptype);
+ if (IS_ENABLED(CONFIG_INET))
+ dev_remove_offload(&pppoe_packet_offload);
unregister_pppox_proto(PX_PROTO_OE);
proto_unregister(&pppoe_sk_proto);
unregister_pernet_device(&pppoe_net_ops);
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index f98e46ae3e30..e6a0c18cc189 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1539,6 +1539,7 @@ struct sk_buff *inet_gro_receive(struct list_head *head, struct sk_buff *skb)

return pp;
}
+EXPORT_INDIRECT_CALLABLE(inet_gro_receive);

static struct sk_buff *ipip_gro_receive(struct list_head *head,
struct sk_buff *skb)
@@ -1624,6 +1625,7 @@ int inet_gro_complete(struct sk_buff *skb, int nhoff)
out:
return err;
}
+EXPORT_INDIRECT_CALLABLE(inet_gro_complete);

static int ipip_gro_complete(struct sk_buff *skb, int nhoff)
{
diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index bd7f780e37a5..32ba4739cef9 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c
@@ -297,6 +297,7 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,

return pp;
}
+EXPORT_INDIRECT_CALLABLE(ipv6_gro_receive);

static struct sk_buff *sit_ip6ip6_gro_receive(struct list_head *head,
struct sk_buff *skb)
@@ -359,6 +360,7 @@ INDIRECT_CALLABLE_SCOPE int ipv6_gro_complete(struct sk_buff *skb, int nhoff)
out:
return err;
}
+EXPORT_INDIRECT_CALLABLE(ipv6_gro_complete);

static int sit_gro_complete(struct sk_buff *skb, int nhoff)
{
--
2.43.0