linux-kernel - Re: [PATCH bpf-next v5 3/3] selftests/bpf: Skip callback tests if jit is disabled in test

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Date: Wed, 17 Jan 2024 17:27:01 -0800
From: Song Liu <song@...nel.org>
To: Hou Tao <houtao@...weicloud.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, John Fastabend <john.fastabend@...il.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 3/3] selftests/bpf: Skip callback tests if jit
 is disabled in test_verifier

Hi,

On Wed, Jan 17, 2024 at 5:11 PM Hou Tao <houtao@...weicloud.com> wrote:
>
> Hi Song,
>
> On 1/18/2024 1:20 AM, Song Liu wrote:
> > On Wed, Jan 17, 2024 at 3:10 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> > [...]
> >> @@ -1622,6 +1624,16 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> >>         alignment_prevented_execution = 0;
> >>
> >>         if (expected_ret == ACCEPT || expected_ret == VERBOSE_ACCEPT) {
> >> +               if (fd_prog < 0 && saved_errno == EINVAL && jit_disabled) {
> >> +                       for (i = 0; i < prog_len; i++, prog++) {
> >> +                               if (!insn_is_pseudo_func(prog))
> >> +                                       continue;
> >> +                               printf("SKIP (callbacks are not allowed in non-JITed programs)\n");
> >> +                               skips++;
> >> +                               goto close_fds;
> >> +                       }
> >> +               }
> >> +
> > I would put this chunk above "alignment_prevented_execution = 0;".
> >
> > @@ -1619,6 +1621,16 @@ static void do_test_single(struct bpf_test
> > *test, bool unpriv,
> >                 goto close_fds;
> >         }
> >
> > +       if (fd_prog < 0 && saved_errno == EINVAL && jit_disabled) {
> > +               for (i = 0; i < prog_len; i++, prog++) {
> > +                       if (!insn_is_pseudo_func(prog))
> > +                               continue;
> > +                       printf("SKIP (callbacks are not allowed in
> > non-JITed programs)\n");
> > +                       skips++;
> > +                       goto close_fds;
> > +               }
> > +       }
> > +
> >         alignment_prevented_execution = 0;
> >
> >         if (expected_ret == ACCEPT || expected_ret == VERBOSE_ACCEPT) {
> >
> > Other than this,
>
> The check was placed before the checking of expected_ret in v3. However
> I suggested Tiezhu to move it after the checking of expected_ret due to

I missed this part while reading the history of the set.

> the following two reasons:
> 1) when the expected result is REJECT, the return value in about one
> third of these test cases is -EINVAL. And I think we should not waste
> the cpu to check the pseudo func and exit prematurely, instead we should
> let test_verifier check expected_err.

I was thinking jit_disabled is not a common use case so that it is OK for
this path to be a little expensive.

> 2) As for now all expected_ret of these failed cases are ACCEPT when jit
> is disabled, so I think it will be enough for current situation and we
> can revise it later if the checking of pseudo func is too later.

That said, I won't object if we ship this version as-is.

Thanks,
Song