linux-kernel - Re: [PATCH 1/6] x86/irq: Add enumeration of NMI source reporting CPU feature

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Date: Wed, 29 May 2024 13:49:40 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, X86 Kernel <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>
Cc: Andi Kleen <andi.kleen@...el.com>, Xin Li <xin3.li@...el.com>
Subject: Re: [PATCH 1/6] x86/irq: Add enumeration of NMI source reporting CPU
 feature

On 5/29/24 13:33, Jacob Pan wrote:
> diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
> index b7d9f530ae16..3f1a1a1961fa 100644
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -84,6 +84,7 @@ static const struct cpuid_dep cpuid_deps[] = {
>   	{ X86_FEATURE_SHSTK,			X86_FEATURE_XSAVES    },
>   	{ X86_FEATURE_FRED,			X86_FEATURE_LKGS      },
>   	{ X86_FEATURE_FRED,			X86_FEATURE_WRMSRNS   },
> +	{ X86_FEATURE_FRED,			X86_FEATURE_NMI_SOURCE},
>   	{}
>   };
>   

This is incorrect. FRED does *not* inherently depend on NMI_SOURCE; the 
dependency is the reverse, but since it *also* depends on FRED being 
dynamically enabled, there is no need to add it to the static table; the 
dynamic test:

> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 4fa0b17e5043..465f04e4a79f 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1427,8 +1427,10 @@ early_param("fred", fred_setup);
>  
>  void __init trap_init(void)
>  {
> -	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
> +	if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred) {
>  		setup_clear_cpu_cap(X86_FEATURE_FRED);
> +		setup_clear_cpu_cap(X86_FEATURE_NMI_SOURCE);
> +	}
>  
>  	/* Init cpu_entry_area before IST entries are set up */
>  	setup_cpu_entry_areas();

.. suffices just fine on its own.

	-hpa