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Message-ID: <293dbe3950a782b8eb3b87b71d7a967e120191fd.camel@gmail.com>
Date: Fri, 14 Mar 2025 15:47:00 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Luis Gerhorst <luis.gerhorst@....de>, Alexei Starovoitov
<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
<andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 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@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
<jolsa@...nel.org>, Puranjay Mohan <puranjay@...nel.org>, Xu Kuohai
<xukuohai@...weicloud.com>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Hari Bathini <hbathini@...ux.ibm.com>,
Christophe Leroy <christophe.leroy@...roup.eu>, Naveen N Rao
<naveen@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, Michael
Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Mykola
Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, Henriette Herzog
<henriette.herzog@....de>, Cupertino Miranda
<cupertino.miranda@...cle.com>, Matan Shachnai <m.shachnai@...il.com>,
Dimitar Kanaliev <dimitar.kanaliev@...eground.com>, Shung-Hsi Yu
<shung-hsi.yu@...e.com>, Daniel Xu <dxu@...uu.xyz>, bpf@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-kselftest@...r.kernel.org, George Guo
<guodongtai@...inos.cn>, WANG Xuerui <git@...0n.name>, Tiezhu Yang
<yangtiezhu@...ngson.cn>
Cc: Maximilian Ott <ott@...fau.de>, Milan Stephan <milan.stephan@....de>
Subject: Re: [PATCH bpf-next 01/11] bpf: Move insn if/else into
do_check_insn()
On Thu, 2025-03-13 at 18:21 +0100, Luis Gerhorst wrote:
> This is required to catch the errors later and fall back to a nospec if
> on a speculative path.
>
> Move code into do_check_insn(), replace
> * "continue" with "return INSN_IDX_MODIFIED"
> * "goto process_bpf_exit" with "return PROCESS_BPF_EXIT"
> * "do_print_state = " with "*do_print_state = "
>
> Signed-off-by: Luis Gerhorst <luis.gerhorst@....de>
> Acked-by: Henriette Herzog <henriette.herzog@....de>
> Cc: Maximilian Ott <ott@...fau.de>
> Cc: Milan Stephan <milan.stephan@....de>
> ---
This refactoring is a long overdue, thank you!
A few nits below.
[...]
> + err = do_check_insn(env, insn, pop_log, &do_print_state, regs, state,
> + &prev_insn_idx);
- `regs` remains declared in do_check(), while nothing prevents
pushing its declaration to do_check_insn().
- `state` is `env->cur_state`, so I'd avoid passing it as a parameter
(just to reduce count);
- `prev_insn_idx` is unused by `do_check_insn`;
- `pop_log` is not used by `do_check_insn`;
- given that `insn` is presumed to correspond to `env->insn_idx` in
many places down the stack not sure about this parameter.
> + if (err < 0) {
> + return err;
> + } else if (err == INSN_IDX_MODIFIED) {
Also, I'd get rid of `INSN_IDX_MODIFIED` and move `env->insn_idx++`
into `do_check_insn()`. This would save a few mental cycles when
looking at the code with full patch-set applied:
} else if (err == INSN_IDX_MODIFIED) {
continue;
} else if (err == PROCESS_BPF_EXIT) {
goto process_bpf_exit;
}
WARN_ON_ONCE(err);
if (state->speculative && cur_aux(env)->nospec_result) {
... bunch of actions ...
}
env->insn_idx++;
One needs to stop for a moment and think why "bunch of actions" is
performed for regular index increment, but not for INSN_IDX_MODIFIED.
> + continue;
> + } else if (err == PROCESS_BPF_EXIT) {
[...]
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