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SubjectRe: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo_x86
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On 2/8/2021 12:56 PM, Borislav Petkov wrote:
> On Mon, Feb 08, 2021 at 07:24:59AM -0800, kan.liang@linux.intel.com 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

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