netdev - Re: [PATCH v2 bpf-next 1/3] bpf: enable BPF_PROG_TEST_RUN for raw

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Date:   Wed, 23 Sep 2020 12:36:12 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: enable BPF_PROG_TEST_RUN for raw_tracepoint

On Wed, Sep 23, 2020 at 9:54 AM Song Liu <songliubraving@...com> wrote:
>
> Add .test_run for raw_tracepoint. Also, introduce a new feature that runs
> the target program on a specific CPU. This is achieved by a new flag in
> bpf_attr.test, cpu_plus. For compatibility, cpu_plus == 0 means run the
> program on current cpu, cpu_plus > 0 means run the program on cpu with id
> (cpu_plus - 1). This feature is needed for BPF programs that handle
> perf_event and other percpu resources, as the program can access these
> resource locally.
>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  include/linux/bpf.h            |  3 ++
>  include/uapi/linux/bpf.h       |  5 ++
>  kernel/bpf/syscall.c           |  2 +-
>  kernel/trace/bpf_trace.c       |  1 +
>  net/bpf/test_run.c             | 88 ++++++++++++++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  5 ++
>  6 files changed, 103 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d7c5a6ed87e30..23758c282eb4b 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1376,6 +1376,9 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
>  int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
>                                      const union bpf_attr *kattr,
>                                      union bpf_attr __user *uattr);
> +int bpf_prog_test_run_raw_tp(struct bpf_prog *prog,
> +                            const union bpf_attr *kattr,
> +                            union bpf_attr __user *uattr);
>  bool btf_ctx_access(int off, int size, enum bpf_access_type type,
>                     const struct bpf_prog *prog,
>                     struct bpf_insn_access_aux *info);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index a22812561064a..89acf41913e70 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -566,6 +566,11 @@ union bpf_attr {
>                                                  */
>                 __aligned_u64   ctx_in;
>                 __aligned_u64   ctx_out;
> +               __u32           cpu_plus;       /* run this program on cpu
> +                                                * (cpu_plus - 1).
> +                                                * If cpu_plus == 0, run on
> +                                                * current cpu.
> +                                                */

the "_plus" part of the name is so confusing, just as off-by-one
semantics.. Why not do what we do with BPF_PROG_ATTACH? I.e., we have
flags field, and if the specific bit is set then we use extra field's
value. In this case, you'd have:

__u32 flags;
__u32 cpu; /* naturally 0-based */

cpu indexing will be natural without any offsets, and you'll have
something like BPF_PROG_TEST_CPU flag, that needs to be specified.
This will work well with backward/forward compatibility. If you need a
special "current CPU" mode, you can achieve that by not specifying
BPF_PROG_TEST_CPU flag, or we can designate (__u32)-1 as a special
"current CPU" value.

WDYT?


>         } test;
>
>         struct { /* anonymous struct used by BPF_*_GET_*_ID */
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index ec68d3a23a2b7..4664531ff92ea 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2975,7 +2975,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
>         }
>  }
>
> -#define BPF_PROG_TEST_RUN_LAST_FIELD test.ctx_out
> +#define BPF_PROG_TEST_RUN_LAST_FIELD test.cpu_plus
>

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