linux-kernel - Re: [PATCH bpf-next v2 2/2] powerpc64/bpf: Inline bpf_get_smp_processor_id() and bpf_get_current

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <37ae675e-dab2-478d-a5a5-17e50679fefa@kernel.org>
Date: Tue, 25 Nov 2025 11:15:03 +0100
From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
To: Saket Kumar Bhaskar <skb99@...ux.ibm.com>, bpf@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc: hbathini@...ux.ibm.com, sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com,
 andrii@...nel.org, eddyz87@...il.com, ast@...nel.org, daniel@...earbox.net,
 martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, naveen@...nel.org, maddy@...ux.ibm.com,
 mpe@...erman.id.au, npiggin@...il.com
Subject: Re: [PATCH bpf-next v2 2/2] powerpc64/bpf: Inline
 bpf_get_smp_processor_id() and bpf_get_current_task()



Le 17/11/2025 à 07:52, Saket Kumar Bhaskar a écrit :
> Inline the calls to bpf_get_smp_processor_id()/bpf_get_current_task()
> in the powerpc bpf jit.
> 
> powerpc saves the Logical processor number (paca_index) and pointer
> to current task (__current) in paca.
> 
> Here is how the powerpc JITed assembly changes after this commit:
> 
> Before:
> 
> cpu = bpf_get_smp_processor_id();
> 
> addis 12, 2, -517
> addi 12, 12, -29456
> mtctr 12
> bctrl
> mr	8, 3
> 
> After:
> 
> cpu = bpf_get_smp_processor_id();
> 
> lhz 8, 8(13)
> 
> To evaluate the performance improvements introduced by this change,
> the benchmark described in [1] was employed.
> 
> +---------------+-------------------+-------------------+--------------+
> |      Name     |      Before       |        After      |   % change   |
> |---------------+-------------------+-------------------+--------------|
> | glob-arr-inc  | 40.701 ± 0.008M/s | 55.207 ± 0.021M/s |   + 35.64%   |
> | arr-inc       | 39.401 ± 0.007M/s | 56.275 ± 0.023M/s |   + 42.42%   |
> | hash-inc      | 24.944 ± 0.004M/s | 26.212 ± 0.003M/s |   +  5.08%   |
> +---------------+-------------------+-------------------+--------------+
> 
> [1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fanakryiko%2Flinux%2Fcommit%2F8dec900975ef&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C4a08a3af41ff4f9bc55d08de25a5f0ee%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638989591794687135%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=FtfTYpm9VgLfO1Q3iZvyrE4QRG317%2B%2BjfPd66Wd%2FQP4%3D&reserved=0
> 
> Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp.c   | 11 +++++++++++
>   arch/powerpc/net/bpf_jit_comp64.c | 10 ++++++++++
>   2 files changed, 21 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 2f2230ae2145..c88dfa1418ec 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -471,6 +471,17 @@ bool bpf_jit_supports_percpu_insn(void)
>   	return IS_ENABLED(CONFIG_PPC64);
>   }
>   
> +bool bpf_jit_inlines_helper_call(s32 imm)
> +{
> +	switch (imm) {
> +	case BPF_FUNC_get_smp_processor_id:
> +	case BPF_FUNC_get_current_task:

What about BPF_FUNC_get_current_task_btf ?

> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
>   void *arch_alloc_bpf_trampoline(unsigned int size)
>   {
>   	return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns);
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 21486706b5ea..4e1643422370 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -1399,6 +1399,16 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
>   		case BPF_JMP | BPF_CALL:
>   			ctx->seen |= SEEN_FUNC;
>   
> +			if (insn[i].src_reg == BPF_REG_0) {

Are you sure you want to use BPF_REG_0 here ? Is it the correct meaning 
? I see RISCV and ARM64 use 0 instead.

If you keep BPF_REG_0 I would have a preference for

		if (src_reg == bpf_to_ppc(BPF_REG_0))

> +				if (imm == BPF_FUNC_get_smp_processor_id) {
> +					EMIT(PPC_RAW_LHZ(insn[i].src_reg, _R13, offsetof(struct paca_struct, paca_index)));

This looks wrong, you can't use insn[i].src_reg to emit powerpc 
instructions, you must use the local src_reg which converts the register 
ID with bpf_to_ppc()

> +					break;
> +				} else if (imm == BPF_FUNC_get_current_task) {
> +					EMIT(PPC_RAW_LD(insn[i].src_reg, _R13, offsetof(struct paca_struct, __current)));

Same here.

> +					break;
> +				}
> +			}
> +
>   			ret = bpf_jit_get_func_addr(fp, &insn[i], extra_pass,
>   						    &func_addr, &func_addr_fixed);
>   			if (ret < 0)