Subject: Re: [PATCH bpf-next] bpf: Remove bpf_get_smp_processor_id_proto
On Mon, 21 Apr 2025 18:53:07 -0700 Alexei Starovoitov
<alexei.starovoi...@gmail.com> wrote:
> On Thu, Apr 17, 2025 at 8:41 PM Feng Yang <yangfeng59...@163.com> wrote:
> >
> > From: Feng Yang <yangf...@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.nakry...@gmail.com>
> > Signed-off-by: Feng Yang <yangf...@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.
>
The following two seem to explain the reason:
https://lore.kernel.org/all/7103e2085afa29c006cd5b94a6e4a2ac83efc30d.1467106475.git.dan...@iogearbox.net/
https://lore.kernel.org/all/02fa71ebe1c560cad489967aa29c653b48932596.1474586162.git.dan...@iogearbox.net/
