netdev - Re: [PATCHv2 bpf-next 3/4] bpf: Resolve symbols with kallsyms_lookup

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Message-ID: <CAEf4Bzau_RmREQwVQ6wPRbCHVXRuAr1k08btaft2jUwBYTeM-Q@mail.gmail.com>
Date:   Wed, 20 Apr 2022 14:49:59 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCHv2 bpf-next 3/4] bpf: Resolve symbols with
 kallsyms_lookup_names for kprobe multi link

On Mon, Apr 18, 2022 at 5:49 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Using kallsyms_lookup_names function to speed up symbols lookup in
> kprobe multi link attachment and replacing with it the current
> kprobe_multi_resolve_syms function.
>
> This speeds up bpftrace kprobe attachment:
>
>   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
>   ...
>   6.5681 +- 0.0225 seconds time elapsed  ( +-  0.34% )
>
> After:
>
>   # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* {  } i:ms:1 { exit(); }'
>   ...
>   0.5661 +- 0.0275 seconds time elapsed  ( +-  4.85% )
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  kernel/trace/bpf_trace.c | 113 +++++++++++++++++++++++----------------
>  1 file changed, 67 insertions(+), 46 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index b26f3da943de..f49cdc46a21f 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2226,6 +2226,60 @@ struct bpf_kprobe_multi_run_ctx {
>         unsigned long entry_ip;
>  };
>
> +struct user_syms {
> +       const char **syms;
> +       char *buf;
> +};
> +
> +static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32 cnt)
> +{
> +       unsigned long __user usymbol;
> +       const char **syms = NULL;
> +       char *buf = NULL, *p;
> +       int err = -EFAULT;
> +       unsigned int i;
> +
> +       err = -ENOMEM;
> +       syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> +       if (!syms)
> +               goto error;
> +
> +       buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> +       if (!buf)
> +               goto error;
> +
> +       for (p = buf, i = 0; i < cnt; i++) {
> +               if (__get_user(usymbol, usyms + i)) {
> +                       err = -EFAULT;
> +                       goto error;
> +               }
> +               err = strncpy_from_user(p, (const char __user *) usymbol, KSYM_NAME_LEN);
> +               if (err == KSYM_NAME_LEN)
> +                       err = -E2BIG;
> +               if (err < 0)
> +                       goto error;
> +               syms[i] = p;
> +               p += err + 1;
> +       }
> +
> +       err = 0;
> +       us->syms = syms;
> +       us->buf = buf;

return 0 here instead of falling through into error: block?

> +
> +error:
> +       if (err) {
> +               kvfree(syms);
> +               kvfree(buf);
> +       }
> +       return err;
> +}
> +
> +static void free_user_syms(struct user_syms *us)
> +{
> +       kvfree(us->syms);
> +       kvfree(us->buf);
> +}
> +
>  static void bpf_kprobe_multi_link_release(struct bpf_link *link)
>  {
>         struct bpf_kprobe_multi_link *kmulti_link;

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