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bpf: make programs see skb->data == L2 for ingress and egress

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eBPF programs attached to ingress and egress qdiscs see inconsistent skb->data.
For ingress L2 header is already pulled, whereas for egress it's present.
This is known to program writers which are currently forced to use
BPF_LL_OFF workaround.
Since programs don't change skb internal pointers it is safe to do
pull/push right around invocation of the program and earlier taps and
later pt->func() will not be affected.
Multiple taps via packet_rcv(), tpacket_rcv() are doing the same trick
around run_filter/BPF_PROG_RUN even if skb_shared.

This fix finally allows programs to use optimized LD_ABS/IND instructions
without BPF_LL_OFF for higher performance.
tc ingress + cls_bpf + samples/bpf/tcbpf1_kern.o
       w/o JIT   w/JIT
before  20.5     23.6 Mpps
after   21.8     26.6 Mpps

Old programs with BPF_LL_OFF will still work as-is.

We can now undo most of the earlier workaround commit:
a166151cbe ("bpf: fix bpf helpers to use skb->mac_header relative offsets")

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
2015-06-04 10:11:53 -07:00
committed by David S. Miller
parent 98da81a426
commit 3431205e03
4 changed files with 30 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
net/sched/act_bpf.c
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@@ -37,6 +37,7 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
{
struct tcf_bpf *prog = act->priv;
int action, filter_res;
bool at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
if (unlikely(!skb_mac_header_was_set(skb)))
return TC_ACT_UNSPEC;
@@ -48,7 +49,13 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
/* Needed here for accessing maps. */
rcu_read_lock();
filter_res = BPF_PROG_RUN(prog->filter, skb);
if (at_ingress) {
__skb_push(skb, skb->mac_len);
filter_res = BPF_PROG_RUN(prog->filter, skb);
__skb_pull(skb, skb->mac_len);
} else {
filter_res = BPF_PROG_RUN(prog->filter, skb);
}
rcu_read_unlock();
/* A BPF program may overwrite the default action opcode.