Re: [PATCH v6 00/90] x86: Introduce a centralized CPUID data model

[Borislav Petkov]

On Wed, May 06, 2026 at 06:59:12AM -0700, H. Peter Anvin wrote:
> Sadly, not true; modutila at least does use these numbers due to the brain
> damaged way that cpu feature modprobe strings was done.

That damn thing!

---
Author: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Date:   Wed May 6 16:43:12 2026 +0200

    x86/cpufeatures: Document that feature numbers can potentially be an ABI
    
    Way too late to change that so document it so that it is written down
    somewhere and not getting forgotten from time to time and the evil
    awakening during development of fancy new things can be spared.
    
    Reported-by: "H. Peter Anvin" <hpa@xxxxxxxxx>
    Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 1d506e5d6f46..5937e2a30da1 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -15,6 +15,10 @@
  *
  * When adding new features here that depend on other features,
  * please update the table in kernel/cpu/cpuid-deps.c as well.
+ *
+ * Note that modutils at least does use these numbers due to the brain-damaged
+ * way that CPU feature modprobe strings was done so the safe assumption is to
+ * think of those as ABI. For that look at do_x86cpu_entry() in file2alias.c.
  */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (EDX), word 0 */


-- 
Regards/Gruss,
    Boris.

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