Re: [PATCH bpf-next] bpf: Remove bpf_get_smp_processor_id_proto

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Thu, Apr 17, 2025 at 8:41 PM Feng Yang <yangfeng59949@163.com> wrote:
>
> From: Feng Yang <yangfeng@kylinos.cn>
>
> All BPF programs either disable CPU preemption or CPU migration,
> so the bpf_get_smp_processor_id_proto can be safely removed,
> and the bpf_get_raw_smp_processor_id_proto in bpf_base_func_proto works perfectly.
>
> Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
> Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
> ---
>  include/linux/bpf.h      |  1 -
>  kernel/bpf/core.c        |  1 -
>  kernel/bpf/helpers.c     | 12 ------------
>  kernel/trace/bpf_trace.c |  2 --
>  net/core/filter.c        |  6 ------
>  5 files changed, 22 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 3f0cc89c0622..36e525141556 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3316,7 +3316,6 @@ extern const struct bpf_func_proto bpf_map_peek_elem_proto;
>  extern const struct bpf_func_proto bpf_map_lookup_percpu_elem_proto;
>
>  extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
> -extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
>  extern const struct bpf_func_proto bpf_get_numa_node_id_proto;
>  extern const struct bpf_func_proto bpf_tail_call_proto;
>  extern const struct bpf_func_proto bpf_ktime_get_ns_proto;
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index ba6b6118cf50..1ad41a16b86e 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2943,7 +2943,6 @@ const struct bpf_func_proto bpf_spin_unlock_proto __weak;
>  const struct bpf_func_proto bpf_jiffies64_proto __weak;
>
>  const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
> -const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
>  const struct bpf_func_proto bpf_get_numa_node_id_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_ns_proto __weak;
>  const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index e3a2662f4e33..2d2bfb2911f8 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -149,18 +149,6 @@ const struct bpf_func_proto bpf_get_prandom_u32_proto = {
>         .ret_type       = RET_INTEGER,
>  };
>
> -BPF_CALL_0(bpf_get_smp_processor_id)
> -{
> -       return smp_processor_id();
> -}
> -
> -const struct bpf_func_proto bpf_get_smp_processor_id_proto = {
> -       .func           = bpf_get_smp_processor_id,
> -       .gpl_only       = false,
> -       .ret_type       = RET_INTEGER,
> -       .allow_fastcall = true,
> -};
> -

bpf_get_raw_smp_processor_id_proto doesn't have
allow_fastcall = true

so this breaks tests.

Instead of removing BPF_CALL_0(bpf_get_smp_processor_id)
we should probably remove BPF_CALL_0(bpf_get_raw_cpu_id)
and adjust SKF_AD_OFF + SKF_AD_CPU case.
I don't recall why raw_ version was used back in 2014.

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