netdev - Re: [PATCH 2/5] bpf: Add bpf_perf_event_output

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Date:   Mon, 6 Jan 2020 15:27:21 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrii Nakryiko <andriin@...com>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Miller <davem@...hat.com>
Subject: Re: [PATCH 2/5] bpf: Add bpf_perf_event_output_kfunc

On Sun, Dec 29, 2019 at 03:37:37PM +0100, Jiri Olsa wrote:
> Adding support to use perf_event_output in
> BPF_TRACE_FENTRY/BPF_TRACE_FEXIT programs.
> 
> There are no pt_regs available in the trampoline,
> so getting one via bpf_kfunc_regs array.
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/trace/bpf_trace.c | 67 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 67 insertions(+)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e5ef4ae9edb5..1b270bbd9016 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1151,6 +1151,69 @@ raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  	}
>  }
>  
> +struct bpf_kfunc_regs {
> +	struct pt_regs regs[3];
> +};
> +
> +static DEFINE_PER_CPU(struct bpf_kfunc_regs, bpf_kfunc_regs);
> +static DEFINE_PER_CPU(int, bpf_kfunc_nest_level);

Thanks a bunch for working on it.

I don't understand why new regs array and nest level is needed.
Can raw_tp_prog_func_proto() be reused as-is?
Instead of patches 2,3,4 ?