Re: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo_x86

[Liang, Kan]

On 2/8/2021 12:56 PM, Borislav Petkov wrote:
> On Mon, Feb 08, 2021 at 07:24:59AM -0800, kan.liang@xxxxxxxxxxxxxxx wrote:
> > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > index c20a52b..1f25ac9 100644
> > --- a/arch/x86/include/asm/processor.h
> > +++ b/arch/x86/include/asm/processor.h
> > @@ -139,6 +139,16 @@ struct cpuinfo_x86 {
> >   	u32			microcode;
> >   	/* Address space bits used by the cache internally */
> >   	u8			x86_cache_bits;
> > +	/*
> > +	 * In hybrid processors, there is a CPU type and a native model ID. The
> > +	 * CPU type (x86_cpu_type[31:24]) describes the type of micro-
> > +	 * architecture families. The native model ID (x86_cpu_type[23:0])
> > +	 * describes a specific microarchitecture version. Combining both
> > +	 * allows to uniquely identify a CPU.
> > +	 *
> > +	 * Please note that the native model ID is not related to x86_model.
> > +	 */
> > +	u32			x86_cpu_type;
>
> Why are you adding it here instead of simply using
> X86_FEATURE_HYBRID_CPU at the call site?
>
> How many uses in this patchset?
>
> /me searches...
>
> Exactly one.
>
> Just query X86_FEATURE_HYBRID_CPU at the call site and read what you
> need from CPUID and use it there - no need for this.

I think it's good enough for perf, but I'm not sure whether other codes 
need the CPU type information.

Ricardo, do you know?

Maybe we should implement a generic function as below for this?
(Not test. Just use as an example.)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a66c1fd..679f5fe 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2056,3 +2056,11 @@ void arch_smt_update(void)
 	/* Check whether IPI broadcasting can be enabled */
 	apic_smt_update();
 }
+
+u32 x86_read_hybrid_type(void)
+{
+	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
+		return cpuid_eax(0x0000001a);
+
+	return 0;
+}


Thanks,
Kan