Re: [PATCH] x86/topo: Map vendor CPU types to generic Linux such types

[Borislav Petkov]

On Wed, Jul 22, 2026 at 11:09:58AM -0700, Pawan Gupta wrote:
> > +enum x86_topology_cpu_type {
> > +	/* X86_CPU_TYPE_ANY */
> > +	TOPO_CPU_TYPE_ANY = 0,
> 
> I don't really understand the purpose of TOPO_CPU_TYPE_ANY here. In the cpu
> matching infrastructure, X86_CPU_TYPE_ANY makes sense. Here I fail to
> understand how is TOPO_CPU_TYPE_ANY different from UNKNOWN? A table passed
> to x86_match_cpu() with X86_CPU_TYPE_ANY entry will match any CPU type
> including TOPO_CPU_TYPE_UNKNOWN.

This will go away in future patches. We do one logical thing per patch and
removing UNKNOWN is not it. I have it on my TODO list to clean up everything
here.

> 
> > +	TOPO_CPU_TYPE_PERFORMANCE,
> > +	TOPO_CPU_TYPE_EFFICIENCY,
> > +	TOPO_CPU_TYPE_UNKNOWN,
> > +};

...

> > @@ -81,7 +53,7 @@ const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id *match)
> >  			continue;
> >  		if (m->feature != X86_FEATURE_ANY && !cpu_has(c, m->feature))
> >  			continue;
> > -		if (!x86_match_vendor_cpu_type(c, m))
> > +		if (m->type != X86_CPU_TYPE_ANY && c->topo.cpu_type != m->type)
> 
> In line with what Thomas pointed that cpu_type is not a system property, I
> suggest matching cpu_type should be dropped from x86_match_cpu(). More so
> because it only uses boot_cpu_data and misses the other types of secondary
> CPUs. I feel it is not a reliable way to match CPU types. Thoughts?

How do you suggest we match CPU types on the whole system?

I.e., "do this workaround only on the performance cores", for example.

c->topo.cpu_type is perfect for that then.

> Slightly unrelated to this patch, on AMD is it that hw_cpu_type only
> available on hybrid systems?

No idea. I will dig through that later, when cleaning up.

If only available on hybrid systems, we will have to fake something there,
X86_CPU_TYPE_ANY perhaps.

:-)

-- 
Regards/Gruss,
    Boris.

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