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

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Message-ID: <75439282-9895-4b17-b6fd-3f0222fa2f03@orca.pet>
Date: Thu, 21 Aug 2025 21:46:42 +0200
From: Marcos Del Sol Vives <marcos@...a.pet>
To: David Laight <david.laight.linux@...il.com>,
 Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 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>, "Ahmed S. Darwish"
 <darwi@...utronix.de>, Kees Cook <kees@...nel.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 21/08/2025 a las 20:40, David Laight escribió:
> On Thu, 21 Aug 2025 14:46:59 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
>> It would mean cloning the page as private. Yes you can do it, uprobes
>> has all the code for this. But it has non-trivial memory overhead.
> 
> I was thinking it would be safe to do this change without cloning the page.
> After all the change is needed for all processes executing the code.
> That might only be easy on UP systems - but I doubt the affected CPU are SMP.
> 
> 	David
> 

Actually...

marcos@...3:~$ nproc
2
marcos@...3:~$ cat /proc/cpuinfo
processor       : 0
vendor_id       : Vortex86 SoC
cpu family      : 6
model           : 1
model name      : Vortex86DX3
stepping        : 1
cpu MHz         : 1000.017
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 0
initial apicid  : 0
fdiv_bug        : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 3
wp              : yes
flags           : fpu pse tsc msr cx8 apic sep pge cmov mmx fxsr sse cpuid
bugs            : itlb_multihit
bogomips        : 2000.03
clflush size    : 32
cache_alignment : 32
address sizes   : 32 bits physical, 32 bits virtual
power management:

processor       : 1
vendor_id       : Vortex86 SoC
cpu family      : 6
model           : 1
model name      : Vortex86DX3
stepping        : 1
cpu MHz         : 1000.017
physical id     : 1
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 1
initial apicid  : 1
fdiv_bug        : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 3
wp              : yes
flags           : fpu pse tsc msr cx8 apic sep pge cmov mmx fxsr sse cpuid
bugs            : itlb_multihit
bogomips        : 2000.03
clflush size    : 32
cache_alignment : 32
address sizes   : 32 bits physical, 32 bits virtual
power management:

Vortex SoCs are true oddballs, aren't they?