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([2620:10d:c090:500::2:d7b1]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b16f16faffsm459465eec.1.2026.01.05.09.45.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Jan 2026 09:45:15 -0800 (PST) Message-ID: <08ab237ad7da8d1f6494cb434d9a5a46a599462c.camel@gmail.com> Subject: Re: [PATCH bpf-next v2 1/2] bpf, x86: inline bpf_get_current_task() for x86_64 From: Eduard Zingerman To: Menglong Dong , ast@kernel.org Cc: davem@davemloft.net, dsahern@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 05 Jan 2026 09:45:13 -0800 In-Reply-To: <20260104131635.27621-2-dongml2@chinatelecom.cn> References: <20260104131635.27621-1-dongml2@chinatelecom.cn> <20260104131635.27621-2-dongml2@chinatelecom.cn> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2026-01-04 at 21:16 +0800, Menglong Dong wrote: > Inline bpf_get_current_task() and bpf_get_current_task_btf() for x86_64 > to obtain better performance. The instruction we use here is: >=20 > 65 48 8B 04 25 [offset] // mov rax, gs:[offset] >=20 > Signed-off-by: Menglong Dong > --- > v2: > - check the variable type in emit_ldx_percpu_r0 with __verify_pcpu_ptr > - remove the usage of const_current_task > --- > arch/x86/net/bpf_jit_comp.c | 36 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 36 insertions(+) >=20 > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index e3b1c4b1d550..f5ff7c77aad7 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -1300,6 +1300,25 @@ static void emit_st_r12(u8 **pprog, u32 size, u32 = dst_reg, int off, int imm) > emit_st_index(pprog, size, dst_reg, X86_REG_R12, off, imm); > } > =20 > +static void __emit_ldx_percpu_r0(u8 **pprog, __force unsigned long ptr) > +{ > + u8 *prog =3D *pprog; > + > + /* mov rax, gs:[ptr] */ > + EMIT2(0x65, 0x48); > + EMIT2(0x8B, 0x04); > + EMIT1(0x25); > + EMIT((u32)ptr, 4); > + > + *pprog =3D prog; > +} > + > +#define emit_ldx_percpu_r0(prog, variable) \ > + do { \ > + __verify_pcpu_ptr(&(variable)); \ > + __emit_ldx_percpu_r0(&prog, (__force unsigned long)&(variable));\ > + } while (0) > + > static int emit_atomic_rmw(u8 **pprog, u32 atomic_op, > u32 dst_reg, u32 src_reg, s16 off, u8 bpf_size) > { > @@ -2441,6 +2460,12 @@ st: if (is_imm8(insn->off)) > case BPF_JMP | BPF_CALL: { > u8 *ip =3D image + addrs[i - 1]; > =20 > + if (insn->src_reg =3D=3D 0 && (insn->imm =3D=3D BPF_FUNC_get_current_= task || > + insn->imm =3D=3D BPF_FUNC_get_current_task_btf)) { I think this should be guarded by IS_ENABLED(CONFIG_SMP). The current.h:get_current() used arch/x86/include/asm/percpu.h:this_cpu_read_stable() that is unrolled to __raw_cpu_read_stable(), which uses __force_percpu_arg(), which uses __force_percpu_prefix, which is defined differently depending on CONFIG_SMP= . > + emit_ldx_percpu_r0(prog, current_task); > + break; > + } > + > func =3D (u8 *) __bpf_call_base + imm32; > if (src_reg =3D=3D BPF_PSEUDO_CALL && tail_call_reachable) { > LOAD_TAIL_CALL_CNT_PTR(stack_depth); > @@ -4082,3 +4107,14 @@ bool bpf_jit_supports_timed_may_goto(void) > { > return true; > } > + > +bool bpf_jit_inlines_helper_call(s32 imm) > +{ > + switch (imm) { > + case BPF_FUNC_get_current_task: > + case BPF_FUNC_get_current_task_btf: > + return true; > + default: > + return false; > + } > +}