linux-kernel - Re: [PATCH 11/11] x86/cpu: Make all all CPUID leaf names consistent

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Message-ID: <20241129182747.GEZ0oHo1eR0l7sREJY@fat_crate.local>
Date: Fri, 29 Nov 2024 19:27:47 +0100
From: Borislav Petkov <bp@...en8.de>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, rafael@...nel.org,
	lenb@...nel.org
Subject: Re: [PATCH 11/11] x86/cpu: Make all all CPUID leaf names consistent

On Thu, Oct 31, 2024 at 10:19:37AM -0700, Dave Hansen wrote:
> >> -#define CPUID_MWAIT_LEAF	0x5
> >> -#define CPUID_DCA_LEAF		0x9
> >> -#define XSTATE_CPUID		0x0d
> >> -#define CPUID_TSC_LEAF		0x15
> >> -#define CPUID_FREQ_LEAF		0x16
> >> -#define TILE_CPUID		0x1d
> >> +#define CPUID_LEAF_MWAIT	0x5
> >> +#define CPUID_LEAF_DCA		0x9
> >> +#define CPUID_LEAF_XSTATE	0x0d
> >> +#define CPUID_LEAF_TSC		0x15
> >> +#define CPUID_LEAF_FREQ		0x16
> >> +#define CPUID_LEAF_TILE		0x1d
> > 
> > ... and just to confuse things even more, there's enum cpuid_leafs too which
> > start with the "CPUID_" prefix too.
> > 
> > Pfff.
> 
> Yeah, lovely.  'enum cpuid_leafs' does appear misnamed though.  It is a
> list of *words*, not actual leaf numbers.  There's also very little
> overlap between those leafs and the newly-renamed ones in this series.
> I think that's because most of the leaves we dump into the CPU caps have
> random feature bits that aren't logically grouped and resist naming.
> 
> The one exception to that is the CPUID_D_1_EAX aka. CPUID_LEAF_XSTATE.
> We could do something like the attached patch, but I don't think it
> really helps much.
> 
> > I'd like to unify them and I *think* kvm_cpu_cap_mask() should be able to
> > stomach that (or fixed if not)...
> 
> Do you mean we could unify the CPUID_8000_0001_EDX enum values and the
> CPUID_LEAF_* defines from this series?

Well, enum cpuid_leafs as it is now is the *indices* into the cap flags array:

struct cpuinfo_x86 {

	...

	__u32           x86_capability[NCAPINTS + NBUGINTS];

And having a "CPUID_" prefixed thing and a "CPUID_LEAF_" prefixed other thing
is going to cause confusion.

And renaming enum cpuid_leafs is going to cause a massive churn...

IOW:

[ Rock ]	<-- us --> 	[ Hard Place ]

:-\

-- 
Regards/Gruss,
    Boris.

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