linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Add some description about BPF_JIT_ALWAYS

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Date:   Fri, 11 Feb 2022 15:44:25 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>
Cc:     Xuefeng Li <lixuefeng@...ngson.cn>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: Add some description about
 BPF_JIT_ALWAYS_ON in Kconfig

On 2/11/22 9:57 AM, Tiezhu Yang wrote:
> When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently
> set to 1 and setting any other value than that will return in failure.
> 
> Add the above description in the help text of BPF_JIT_ALWAYS_ON, and then
> we can distinguish between BPF_JIT_ALWAYS_ON and BPF_JIT_DEFAULT_ON.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   kernel/bpf/Kconfig | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> index d24d518..88409f8 100644
> --- a/kernel/bpf/Kconfig
> +++ b/kernel/bpf/Kconfig
> @@ -58,6 +58,9 @@ config BPF_JIT_ALWAYS_ON
>   	  Enables BPF JIT and removes BPF interpreter to avoid speculative
>   	  execution of BPF instructions by the interpreter.
>   
> +	  When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently
> +	  set to 1 and setting any other value than that will return in failure.

Small nit here: lets use the full path (/proc/sys/net/core/bpf_jit_enable) in order
to be consistent with the other descriptions in this Kconfig.

>   config BPF_JIT_DEFAULT_ON
>   	def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON
>   	depends on HAVE_EBPF_JIT && BPF_JIT
>