linux-kernel - Re: nop5-optimized USDTs WAS: Re: [PATCHv6 perf/core 09/22] uprobes/x86: Add uprobe syscall to speed up uprobe

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Message-ID: <CAEf4BzaHcs2wa_F4ro4Lg31WX-7+uo=CGpUKUD_2MfhGEAvazQ@mail.gmail.com>
Date: Wed, 10 Sep 2025 10:30:39 -0400
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <olsajiri@...il.com>, Oleg Nesterov <oleg@...hat.com>, 
	Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>, 
	open list <linux-kernel@...r.kernel.org>, 
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>, 
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, Hao Luo <haoluo@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, 
	Thomas Weißschuh <thomas@...ch.de>, 
	Ingo Molnar <mingo@...nel.org>
Subject: Re: nop5-optimized USDTs WAS: Re: [PATCHv6 perf/core 09/22]
 uprobes/x86: Add uprobe syscall to speed up uprobe

On Fri, Sep 5, 2025 at 4:24 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Sep 04, 2025 at 11:58:26PM +0200, Peter Zijlstra wrote:
> > On Thu, Sep 04, 2025 at 11:56:17PM +0200, Peter Zijlstra wrote:
> >
> > > Ooh, that suggests we do something like so:
> >
> > N/m, I need to go sleep, that doesn't work right for the 32bit nops that
> > use lea instead of nopl. I'll see if I can come up with something more
> > sensible.
>
> Something like this. Can someone please look very critical at this fancy
> insn_is_nop()?

Can't truly review that low-level instruction decoding logic (and you
seem to have found an issue yourself), but superficially the cases
that are claimed to be handled seem like legit no-op instructions. And
the overall logic of nop handling in can_optimize and emulation seems
to be intact as well.

Thanks for generalizing all this!

To the extent that this means anything:

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>
> ---
>  arch/x86/include/asm/insn-eval.h |  2 +
>  arch/x86/kernel/alternative.c    | 20 +--------
>  arch/x86/kernel/uprobes.c        | 32 ++------------
>  arch/x86/lib/insn-eval.c         | 92 ++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 98 insertions(+), 48 deletions(-)
>

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