linux-kernel - Re: [PATCH -v3 0/15] x86: Remove support for TSC-less and CX8-less CPUs

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Message-ID: <8cb799cb-a3ff-4257-b03d-661b893a2663@zytor.com>
Date: Tue, 6 Jan 2026 19:57:22 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Borislav Petkov <bp@...en8.de>, "Ahmed S. Darwish" <darwi@...utronix.de>
Cc: Brian Gerst <brgerst@...il.com>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH -v3 0/15] x86: Remove support for TSC-less and CX8-less
 CPUs

On 2026-01-04 05:08, Borislav Petkov wrote:
> On Mon, Dec 15, 2025 at 02:55:27PM +0100, Ahmed S. Darwish wrote:
>> If it does, then we can also remove X86_FEATURE_CPUID from word 3:
>>
>> --- linux.orig/arch/x86/include/asm/cpufeatures.h
>> +++ linux/arch/x86/include/asm/cpufeatures.h
>> @@ -94,3 +94,3 @@
>>  #define X86_FEATURE_NONSTOP_TSC	( 3*32+24) /* "nonstop_tsc" TSC does not stop in C states */
>> -#define X86_FEATURE_CPUID		( 3*32+25) /* "cpuid" CPU has CPUID instruction itself */
>> +/* Reserved				( 3*32+25) */
> 
> s/Reserved/Free/
> 
> so that it gets reused.
> 

Please DON'T do this.

I have been cleaning up the boot code and it turns out that having this flag
available makes the error message generating code in the boot stub a lot nicer.

	-hpa