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

On Fri, Mar 27, 2026 at 03:15:14AM +0100, Ahmed S. Darwish wrote:
> For the Linux-synthetic feature words, only x86_capability[] defines them
> as they have no hardware backing.  Unify their handling by defining them in
> x86-cpuid-db as a synthetic CPUID leaf:
> 
> <leaf id="0x4c780001">
>   <desc>Linux-defined synthetic feature flags</desc>

Hmm, this makes me wonder: we have cases where we take a x86_capability
element which mirrors a real CPUID reg and then turn it into a synthetic word
because we end up using only a handful of the real bits and there's no need to
have almost unused word.

Example:

ddde4abaa0ec ("x86/cpufeatures: Make X86_FEATURE leaf 17 Linux-specific")

I guess I'll see what happens when I reach the end of the patchset - I'm just
pointing this out now, before I forget so that we don't shoot ourselves in the
foot ABI-wise and for no good reason.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette