linux-kernel - Re: [PATCH bpf-next] riscv, bpf: Optimize stack usage of trampoline

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Message-ID: <d9abcecb-1de1-4c88-923a-b465fb87ca51@huawei.com>
Date: Mon, 8 Jul 2024 20:02:06 +0800
From: Pu Lehui <pulehui@...wei.com>
To: Puranjay Mohan <puranjay@...nel.org>
CC: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
	<martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu
	<song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend
	<john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev
	<sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Björn Töpel <bjorn@...nel.org>, Puranjay Mohan
	<puranjay12@...il.com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
 Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
	<bpf@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] riscv, bpf: Optimize stack usage of trampoline


On 2024/7/8 19:47, Puranjay Mohan wrote:
> When BPF_TRAMP_F_CALL_ORIG is not set, stack space for passing arguments
> on stack doesn't need to be reserved because the original function is
> not called.
> 
> Only reserve space for stacked arguments when BPF_TRAMP_F_CALL_ORIG is
> set.
> 
> Signed-off-by: Puranjay Mohan <puranjay@...nel.org>
> ---
>   arch/riscv/net/bpf_jit_comp64.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 685c7389ae7e..0795efdd3519 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -892,7 +892,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
>   	stack_size += 8;
>   	sreg_off = stack_size;
>   
> -	if (nr_arg_slots - RV_MAX_REG_ARGS > 0)
> +	if ((flags & BPF_TRAMP_F_CALL_ORIG) && (nr_arg_slots - RV_MAX_REG_ARGS > 0))
>   		stack_size += (nr_arg_slots - RV_MAX_REG_ARGS) * 8;
>   
>   	stack_size = round_up(stack_size, STACK_ALIGN);

Thanks!

Acked-by: Pu Lehui <pulehui@...wei.com>