linux-kernel - Re: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo

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Date:   Mon, 8 Feb 2021 14:04:24 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     peterz@...radead.org, acme@...nel.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        namhyung@...nel.org, jolsa@...hat.com, ak@...ux.intel.com,
        yao.jin@...ux.intel.com, alexander.shishkin@...ux.intel.com,
        adrian.hunter@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <len.brown@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 02/49] x86/cpu: Describe hybrid CPUs in cpuinfo_x86



On 2/8/2021 12:56 PM, Borislav Petkov wrote:
> On Mon, Feb 08, 2021 at 07:24:59AM -0800, kan.liang@...ux.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