linux-kernel - Re: [PATCH bpf-next 2/2] bpf: Make BPF_JIT_DEFAULT

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Message-ID: <65323db1-5fcb-21b3-2197-9bd6935bd96c@loongson.cn>
Date:   Sat, 12 Feb 2022 10:40:26 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Daniel Borkmann <daniel@...earbox.net>,
        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 2/2] bpf: Make BPF_JIT_DEFAULT_ON selectable in
 Kconfig

On 02/11/2022 06:23 PM, Daniel Borkmann wrote:
> On 2/11/22 9:57 AM, Tiezhu Yang wrote:
>> Currently, it is not possible to set bpf_jit_enable to 1 by default
>> and the users can change it to 0 or 2, it seems bad for some users,
>> make BPF_JIT_DEFAULT_ON selectable to give them a chance.
>
> I'm not fully sure I follow the above, so you are saying that a kconfig of
> !BPF_JIT_ALWAYS_ON and ARCH_WANT_DEFAULT_BPF_JIT, enables
> BPF_JIT_DEFAULT_ON
> however in such setting you are not able to reset bpf_jit_enable back to
> 0 at
> runtime?

Oh, no. Sorry for the unclear description.

currently, only x86, arm64 and s390 select ARCH_WANT_DEFAULT_BPF_JIT,
the other archs do not select ARCH_WANT_DEFAULT_BPF_JIT. On the archs
without ARCH_WANT_DEFAULT_BPF_JIT, if we want to set bpf_jit_enable to
1 by default, the only way is to enable CONFIG_BPF_JIT_ALWAYS_ON, then
the users can not change it to 0 or 2, it seems bad for some users, we
can select ARCH_WANT_DEFAULT_BPF_JIT for those archs if it is proper,
but at least for now, make BPF_JIT_DEFAULT_ON selectable can give them
a chance.

Additionaly, with this patch, under !BPF_JIT_ALWAYS_ON, we can disable
BPF_JIT_DEFAULT_ON on the archs with ARCH_WANT_DEFAULT_BPF_JIT when
make menuconfig, it seems flexible for some developers.

If you are OK, I will update the commit message and then send v2.

Thanks,
Tiezhu

>
> Thanks,
> Daniel