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Date:   Fri, 14 Apr 2023 12:48:08 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
Cc:     tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org,
        peterz@infradead.org, seanjc@google.com, pbonzini@redhat.com,
        kim.phillips@amd.com, babu.moger@amd.com,
        pawan.kumar.gupta@linux.intel.com, sandipan.das@amd.com,
        CobeChen@zhaoxin.com, TimGuo@zhaoxin.com, LeoLiu-oc@zhaoxin.com
Subject: Re: [PATCH] x86/cpufeatures: extend CPUID leaf 0xc0000001 support
 for Zhaoxin
Message-ID: <20230414104808.GBZDkvaJechZSM+SI9@fat_crate.local>
References: <20230414095334.8743-1-TonyWWang-oc@zhaoxin.com>
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On Fri, Apr 14, 2023 at 05:53:34PM +0800, Tony W Wang-oc wrote:
> Extend CPUID leaf 0xc0000001 to support SM2, SM3, SM4, PARALLAX, TM3,
> RNG2, PHE2, RSA.
> 
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 0]  SM2
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 1]  SM2_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 4]  SM3 SM4
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 5]  SM3_EN SM4_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 16] PARALLAX
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 17] PARALLAX_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 20] TM3
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 21] TM3_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 22] RNG2
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 23] RNG2_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 25] PHE2
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 26] PHE2_EN
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 27] RSA
> CPUID.(EAX=0xc0000001,ECX=0):EDX[bit 28] RSA_EN

None of those flags are used in code, why do we need this patch?

If you want to dump them on the hardware to know what's set or not,
there's tools/arch/x86/kcpuid/ for that.

> SM2/SM3/SM4 imply the instructions support for Chinese cipher security
> algorithm generations 2/3/4.
> PARALLAX is the feature of Zhaoxin CPU that automatically adjusts
> processors's voltage as a function of temperature.
> TM3 is the abbreviation of Thermal Monitor version 3.
> RNG2 is the abbreviation of Random Number Generation version 2.
> PHE2 is the abbreviation of Padlock Hash Engine version 2.
> RSA implies Zhaoxin hardware support for RSA algorithm.
> 
> All these features have two relative CPUID bits, one bit implies the
> existence of the feature and the other bit with postfix "EN" implies
> the availability of this feature.

That's a lot of waste of CPUID bits but that's your decision.

-- 
Regards/Gruss,
    Boris.

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