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

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Message-ID: <be242e65-b056-4e12-93e7-9a297aaf231a@orca.pet>
Date: Wed, 20 Aug 2025 11:51:27 +0200
From: Marcos Del Sol Vives <marcos@...a.pet>
To: 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>, Kees Cook <kees@...nel.org>,
 "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

El 20/08/2025 a las 11:43, Borislav Petkov escribió:
> On Wed, Aug 20, 2025 at 11:33:05AM +0200, Marcos Del Sol Vives wrote:
>> But I think the kernel should let the user know the binaries they're
>> running are having some performance penalty due to this emulation, in case
>> they want to recompile without the offending flags.
> 
> Sure, once perhaps.
> 
> Do you want to let the user know for each binary?
> 
> And how many users do you really think will look at dmesg and recompile their
> binaries?

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.

A global flag would mean they'd need to reboot to see if there is any other
binary triggering it too.

Whether they look or not at the dmesg I cannot tell, but if IOPL emulation
does logging this way, I assumed this should too. Otherwise, would that
mean IOPL emulation logging is also too verbose?