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

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Message-ID: <aUATT37rXDPXKYyH@lx-t490>
Date: Mon, 15 Dec 2025 14:55:27 +0100
From: "Ahmed S. Darwish" <darwi@...utronix.de>
To: Brian Gerst <brgerst@...il.com>
Cc: 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>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...or.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

Hi,

On Sun, 14 Dec 2025, Brian Gerst wrote:
>
> Does this also eliminate all processors that do not support CPUID?
>

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) */
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* "extd_apicid" Extended APICID (8 bits) */

plus its call sites.

Thanks,
Ahmed