linux-kernel - Re: [PATCH bpf-next v5 1/2] bpf, x86: inline bpf_get_current_task() for x86

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Message-ID: <e2403635a55fcf95e3d2aac7c0606388a62c713a.camel@gmail.com>
Date: Mon, 19 Jan 2026 12:43:17 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>, ast@...nel.org
Cc: daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org, 
	martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
 kpsingh@...nel.org, 	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
 bpf@...r.kernel.org, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 1/2] bpf, x86: inline bpf_get_current_task()
 for x86_64

On Mon, 2026-01-19 at 15:02 +0800, Menglong Dong wrote:
> Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64
                                                                   ^^^^^^
					Nit: this change is no longer x86 specific.

> to obtain better performance.
> 
> In !CONFIG_SMP case, the percpu variable is just a normal variable, and
> we can read the current_task directly.
> 
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>

Acked-by: Eduard Zingerman <eddyz87@...il.com>

[...]

> @@ -23319,6 +23323,24 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
>  			insn      = new_prog->insnsi + i + delta;
>  			goto next_insn;
>  		}
> +
> +		/* Implement bpf_get_current_task() and bpf_get_current_task_btf() inline. */
> +		if ((insn->imm == BPF_FUNC_get_current_task || insn->imm == BPF_FUNC_get_current_task_btf) &&
> +		    verifier_inlines_helper_call(env, insn->imm)) {
> +			insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&current_task);
> +			insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> +			insn_buf[2] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0);
                                                 ^^^^^^^
			Silly question:
			  This assumes pointer size of 8 bytes.
			  Which is true for all archs where bpf_jit_supports_percpu_insn()
			  returns true at the moment. Do we want an additional safety check
			  here?

> +			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 &&