linux-kernel - Re: [PATCH] x86: add hintable NOPs emulation

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Message-ID: <19EDD0A4-9466-4D5F-B312-BCA293AC660E@kernel.org>
Date: Wed, 20 Aug 2025 19:00:52 -0700
From: Kees Cook <kees@...nel.org>
To: Marcos Del Sol Vives <marcos@...a.pet>, Borislav Petkov <bp@...en8.de>
CC: "Ahmed S. Darwish" <darwi@...utronix.de>, linux-kernel@...r.kernel.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
 Uros Bizjak <ubizjak@...il.com>, Ard Biesheuvel <ardb@...nel.org>,
 David Kaplan <david.kaplan@....com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Andrew Cooper <andrew.cooper3@...rix.com>, Oleg Nesterov <oleg@...hat.com>,
 "Xin Li (Intel)" <xin@...or.com>, Sabyrzhan Tasbolatov <snovitoll@...il.com>
Subject: Re: [PATCH] x86: add hintable NOPs emulation

On August 20, 2025 3:01:30 AM PDT, Marcos Del Sol Vives <marcos@...a.pet> wrote:
>El 20/08/2025 a las 11:55, Borislav Petkov escribió:
>> On Wed, Aug 20, 2025 at 11:51:27AM +0200, Marcos Del Sol Vives wrote:
>>> I mean, they should know what they need to recompile if they want to, not
>>> just that their machine is having a bug triggered by some binary.
>> 
>> And what's stopping you from writing a proper error message explaining that?
>> 
>> And issuing that error message *exactly once* instead of flooding dmesg for no
>> good reason?
>
>Please define "once". Once per what? Per boot? Per executable? Per process?
>
>Once per boot would mean they'd need to reboot to see if any other executables
>are affected. Per executable AFAIK there are no facilities to do that, and the
>closest is per process which is what it's currently being done (again, like
>IOPL emulation which was already deemed okay a couple years ago and merged
>into the kernel)

If they want to see them again, just: 

echo 1 >/sys/kernel/debug/clear_warn_once

-- 
Kees Cook