RE: [PATCH v2 bpf-next 2/4] bpf: inline bpf_get_smp_processor_id() helper

[John Fastabend <john.fastabend@gmail.com>]

Andrii Nakryiko wrote:
> If BPF JIT supports per-CPU MOV instruction, inline bpf_get_smp_processor_id()
> to eliminate unnecessary function calls.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  kernel/bpf/verifier.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index edb650667f44..af0274b090bb 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20072,6 +20072,30 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  			goto next_insn;
>  		}
>  
> +#ifdef CONFIG_X86_64
> +		/* Implement bpf_get_smp_processor_id() inline. */
> +		if (insn->imm == BPF_FUNC_get_smp_processor_id &&
> +		    prog->jit_requested && bpf_jit_supports_percpu_insn()) {
> +			/* BPF_FUNC_get_smp_processor_id inlining is an
> +			 * optimization, so if pcpu_hot.cpu_number is ever
> +			 * changed in some incompatible and hard to support
> +			 * way, it's fine to back out this inlining logic
> +			 */
> +			insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
> +			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> +			insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
> +			cnt = 3;
> +
> +			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
> +			if (!new_prog)
> +				return -ENOMEM;
> +
> +			delta    += cnt - 1;
> +			env->prog = prog = new_prog;
> +			insn      = new_prog->insnsi + i + delta;
> +			goto next_insn;
> +		}
> +#endif
>  		/* Implement bpf_get_func_arg inline. */
>  		if (prog_type == BPF_PROG_TYPE_TRACING &&
>  		    insn->imm == BPF_FUNC_get_func_arg) {
> -- 
> 2.43.0
> 
> 

Acked-by: John Fastabend <john.fastabend@gmail.com>