linux-kernel - Re: [PATCH RFC v2a 5/9] x86/cpufeatures: Add X86_FEATURE

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Message-ID: <7b91d929-fe97-44c6-aa94-05417bce1014@intel.com>
Date: Fri, 11 Apr 2025 11:23:32 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, <linux-kernel@...r.kernel.org>
CC: <x86@...nel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH RFC v2a 5/9] x86/cpufeatures: Add X86_FEATURE_APX

On 4/11/2025 9:54 AM, Sohil Mehta wrote:
> On 4/11/2025 9:12 AM, Chang S. Bae wrote:
> 
>> +#define X86_FEATURE_APX			(21*32 + 9) /* Advanced #Performance Extensions */
> 
> Is the '#' before 'Performance' intentional? The previous version didn't
> seem to have it.

Oh no — I only meant to update the bit position. My bad!
> I don't think this table follows any specific logic, but recent patches
> have tried grouping by similar features or features with similar
> dependencies.
> 
> I don't have a preference, but should this be inserted closer to other
> XSAVE dependent features?
> 
>      { X86_FEATURE_PKU,                      X86_FEATURE_XSAVE     },
>      { X86_FEATURE_MPX,                      X86_FEATURE_XSAVE     },
>      { X86_FEATURE_XGETBV1,                  X86_FEATURE_XSAVE     },
> +   { X86_FEATURE_APX,                      X86_FEATURE_XSAVE     },
>      { X86_FEATURE_CMOV,                     X86_FEATURE_FXSR      },

> There is a comment on top of that table that says:
> "Please keep the leaf sorted by cpuid_bit.level for faster search."
> 
> Based on that, APX should be inserted here:
> 
>   { X86_FEATURE_INTEL_PPIN,               CPUID_EBX,  0, 0x00000007, 1 },
> +{ X86_FEATURE_APX,                      CPUID_EDX, 21, 0x00000007, 1 },
>   { X86_FEATURE_RRSBA_CTRL,               CPUID_EDX,  2, 0x00000007, 2 },Yeah, both suggestions make sense. Thanks for pointing them out!

I've attached the patch revision.

Thanks,
Chang



View attachment "0005-x86-cpufeatures-Add-X86_FEATURE_APX.patch" of type "text/plain" (3234 bytes)