Re: [PATCH net-next v2 2/3] net: gro: parse ipv6 ext headers without frag0 invalidation

On Tue, Jan 2, 2024 at 2:25 PM Richard Gobert richardbgobert@gmail.com wrote:

The existing code always pulls the IPv6 header and sets the transport offset initially. Then optionally again pulls any extension headers in ipv6_gso_pull_exthdrs and sets the transport offset again on return from that call. skb->data is set at the start of the first extension header before calling ipv6_gso_pull_exthdrs, and must disable the frag0 optimization because that function uses pskb_may_pull/pskb_pull instead of skb_gro_ helpers. It sets the GRO offset to the TCP header with skb_gro_pull and sets the transport header. Then returns skb->data to its position before this block.

This commit introduces a new helper function - ipv6_gro_pull_exthdrs - which is used in ipv6_gro_receive to pull ipv6 ext headers instead of ipv6_gso_pull_exthdrs. Thus, there is no modification of skb->data, all operations use skb_gro_* helpers, and the frag0 fast path can be taken for IPv6 packets with ext headers.

Signed-off-by: Richard Gobert richardbgobert@gmail.com Reviewed-by: Willem de Bruijn willemb@google.com

---

include/net/ipv6.h | 1 + net/ipv6/ip6_offload.c | 51 +++++++++++++++++++++++++++++++++--------- 2 files changed, 42 insertions(+), 10 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h index 78d38dd88aba..217240efa182 100644 --- a/include/net/ipv6.h +++ b/include/net/ipv6.h @@ -26,6 +26,7 @@ struct ip_tunnel_info; #define SIN6_LEN_RFC2133 24

#define IPV6_MAXPLEN 65535 +#define IPV6_MIN_EXTHDR_LEN 8

// Hmm see my following comment.

/*

• NextHeader field of IPv6 header
  

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c index 0e0b5fed0995..c07111d8f56a 100644 --- a/net/ipv6/ip6_offload.c +++ b/net/ipv6/ip6_offload.c @@ -37,6 +37,40 @@ INDIRECT_CALL_L4(cb, f2, f1, head, skb); \ })

+static int ipv6_gro_pull_exthdrs(struct sk_buff *skb, int off, int proto) +{

•   const struct net_offload *ops = NULL;
  

•   struct ipv6_opt_hdr *opth;
  

•   for (;;) {
  

•           int len;
  

•           ops = rcu_dereference(inet6_offloads[proto]);
  

•           if (unlikely(!ops))
  

•                   break;
  

•           if (!(ops->flags & INET6_PROTO_GSO_EXTHDR))
  

•                   break;
  

•           opth = skb_gro_header(skb, off + IPV6_MIN_EXTHDR_LEN, off);
  

I do not see a compelling reason for adding yet another constant here.

I would stick to

opth = skb_gro_header(skb, off + sizeof(*opth), off);

Consistency with similar helpers is desirable.

•           if (unlikely(!opth))
  

•                   break;
  

•           len = ipv6_optlen(opth);
  

•           opth = skb_gro_header(skb, off + len, off);
  

Note this call will take care of precise pull.

•           if (unlikely(!opth))
  

•                   break;
  

•           proto = opth->nexthdr;
  

•           off += len;
  

•   }
  

•   skb_gro_pull(skb, off - skb_network_offset(skb));
  

•   return proto;
  

+}

static int ipv6_gso_pull_exthdrs(struct sk_buff *skb, int proto) { const struct net_offload *ops = NULL; @@ -203,28 +237,25 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head, goto out;

    skb_set_network_header(skb, off);

•   skb_gro_pull(skb, sizeof(*iph));
  

•   skb_set_transport_header(skb, skb_gro_offset(skb));
  
  

•   flush += ntohs(iph->payload_len) != skb_gro_len(skb);
  

•   flush += ntohs(iph->payload_len) != skb->len - hlen;
  
    proto = iph->nexthdr;
    ops = rcu_dereference(inet6_offloads[proto]);
    if (!ops || !ops->callbacks.gro_receive) {
  

•           pskb_pull(skb, skb_gro_offset(skb));
  

•           skb_gro_frag0_invalidate(skb);
  

•           proto = ipv6_gso_pull_exthdrs(skb, proto);
  

•           skb_gro_pull(skb, -skb_transport_offset(skb));
  

•           skb_reset_transport_header(skb);
  

•           __skb_push(skb, skb_gro_offset(skb));
  

•           proto = ipv6_gro_pull_exthdrs(skb, hlen, proto);
  
            ops = rcu_dereference(inet6_offloads[proto]);
            if (!ops || !ops->callbacks.gro_receive)
                    goto out;
  
  

•           iph = ipv6_hdr(skb);
  

•           iph = skb_gro_network_header(skb);
  

•   } else {
  

•           skb_gro_pull(skb, sizeof(*iph));
    }
  
  

•   skb_set_transport_header(skb, skb_gro_offset(skb));
  

•   NAPI_GRO_CB(skb)->proto = proto;
  
    flush--;
  

-- 2.36.1