netdev - Re: [PATCH bpf 2/2] bpf: selftest to verify mixing bpf2bpf calls and tailcalls with insn patch

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Message-ID: <60c0eb99aa8c2_98621208ad@john-XPS-13-9370.notmuch>
Date:   Wed, 09 Jun 2021 09:26:01 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andriin@...com,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf 2/2] bpf: selftest to verify mixing bpf2bpf calls and
 tailcalls with insn patch

Maciej Fijalkowski wrote:
> On Tue, Jun 08, 2021 at 12:30:33PM -0700, John Fastabend wrote:
> > This adds some extra noise to the tailcall_bpf2bpf4 tests that will cause
> > verifier to patch insns. This then moves around subprog start/end insn
> > index and poke descriptor insn index to ensure that verify and JIT will
> > continue to track these correctly.
> 
> This test is the most complicated one where I tried to document the scope
> of it on the side of prog_tests/tailcalls.c. I feel that it would make it
> more difficult to debug it if under any circumstances something would have
> been broken with that logic.
> 
> Maybe a separate test scenario? Or is this an overkill? If so, I would
> vote for moving it to tailcall_bpf2bpf1.c and have a little comment that
> testing other bpf helpers mixed in is in scope of that test.

I like pushing it into the complex test to get the most instruction
patching combinations possible.

> 
> > 
> > Reviewed-by: Daniel Borkmann <daniel@...earbox.net>
> > Signed-off-by: John Fastabend <john.fastabend@...il.com>
> > ---
> >  .../selftests/bpf/progs/tailcall_bpf2bpf4.c        |   17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> > index 9a1b166b7fbe..0d70de5f97e2 100644
> > --- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> > +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf4.c
> > @@ -2,6 +2,13 @@
> >  #include <linux/bpf.h>
> >  #include <bpf/bpf_helpers.h>
> >  
> > +struct {
> > +	__uint(type, BPF_MAP_TYPE_ARRAY);
> > +	__uint(max_entries, 1);
> > +	__uint(key_size, sizeof(__u32));
> > +	__uint(value_size, sizeof(__u32));
> > +} nop_table SEC(".maps");
> > +
> >  struct {
> >  	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
> >  	__uint(max_entries, 3);
> > @@ -11,9 +18,19 @@ struct {
> >  
> >  static volatile int count;
> >  
> > +__noinline
> > +int subprog_noise(struct __sk_buff *skb)
> > +{
> > +	__u32 key = 0;
> > +
> > +	bpf_map_lookup_elem(&nop_table, &key);
> > +	return 0;
> > +}
> > +
> >  __noinline
> >  int subprog_tail_2(struct __sk_buff *skb)
> >  {
> > +	subprog_noise(skb);
> >  	bpf_tail_call_static(skb, &jmp_table, 2);
> >  	return skb->len * 3;
> >  }
> > 
> >