linux-kernel - Re: [PATCH 2/4] x86/cpufeatures: Add AMD feature bits for Prediction Command

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Date:   Sun, 21 Jan 2018 13:16:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     David Woodhouse <dwmw@...zon.co.uk>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org
Subject: Re: [PATCH 2/4] x86/cpufeatures: Add AMD feature bits for Prediction
 Command

On Sat, Jan 20, 2018 at 12:03:31PM +0000, David Woodhouse wrote:
> AMD doesn't implement the Speculation Control MSR that Intel does, but
> the Prediction Control MSR does exist and is advertised by a separate
> CPUID bit. Add support for that.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index adebdaa..624d978 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -207,6 +207,7 @@
>  #define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* AMD Retpoline mitigation for Spectre variant 2 */
>  #define X86_FEATURE_INTEL_PPIN		( 7*32+14) /* Intel Processor Inventory Number */
>  
> +#define X86_FEATURE_AMD_PRED_CMD	( 7*32+17) /* Prediction Command MSR (AMD) */

Right, so this bit I've seen being called differently. Tom, can you
clarify pls?

Also, public ZN PPR says about it:

CPUID_Fn80000007_EDX [Advanced Power Management Information] (ApmInfoEdx)
...

12 ApmPwrReporting: APM power reporting. Read-only. Reset: Fixed,0.

so I'm guessing it has been repurposed or so as APM is not used anymore?

Leaving in the rest for reference.

>  #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
>  #define X86_FEATURE_RSB_CTXSW		( 7*32+19) /* Fill RSB on context switches */
>  
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index df11f5d..c76009e 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -28,6 +28,7 @@ static const struct cpuid_bit cpuid_bits[] = {
>  	{ X86_FEATURE_HW_PSTATE,	CPUID_EDX,  7, 0x80000007, 0 },
>  	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
>  	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
> +	{ X86_FEATURE_AMD_PRED_CMD,	CPUID_EDX, 12, 0x80000007, 0 },
>  	{ X86_FEATURE_SME,		CPUID_EAX,  0, 0x8000001f, 0 },
>  	{ 0, 0, 0, 0, 0 }
>  };
> -- 
> 2.7.4
> 

-- 
Regards/Gruss,
    Boris.

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