linux-kernel - Re: [RFC v2 4/9] x86/mm: Introduce X86_FEATURE

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Message-ID: <20250521115343.GCaC2-x8LsmMApUkjQ@fat_crate.local>
Date: Wed, 21 May 2025 13:53:43 +0200
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
	kernel-team@...a.com, dave.hansen@...ux.intel.com, luto@...nel.org,
	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, nadav.amit@...il.com, Rik van Riel <riel@...com>,
	Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [RFC v2 4/9] x86/mm: Introduce X86_FEATURE_RAR

On Mon, May 19, 2025 at 09:02:29PM -0400, Rik van Riel wrote:
> From: Rik van Riel <riel@...com>
> 
> Introduce X86_FEATURE_RAR and enumeration of the feature.
> 
> [riel: moved initialization to intel.c and disabling to Kconfig.cpufeatures]
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>

I'm guessing Yu-cheng is the original author - that's expressed differently.

> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  arch/x86/Kconfig.cpufeatures       |  4 ++++
>  arch/x86/include/asm/cpufeatures.h |  2 +-
>  arch/x86/kernel/cpu/common.c       | 13 +++++++++++++
>  3 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
> index 250c10627ab3..7d459b5f47f7 100644
> --- a/arch/x86/Kconfig.cpufeatures
> +++ b/arch/x86/Kconfig.cpufeatures
> @@ -195,3 +195,7 @@ config X86_DISABLED_FEATURE_SEV_SNP
>  config X86_DISABLED_FEATURE_INVLPGB
>  	def_bool y
>  	depends on !BROADCAST_TLB_FLUSH
> +
> +config X86_DISABLED_FEATURE_RAR
> +	def_bool y
> +	depends on !BROADCAST_TLB_FLUSH
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 5b50e0e35129..0729c2d54109 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -76,7 +76,7 @@
>  #define X86_FEATURE_K8			( 3*32+ 4) /* Opteron, Athlon64 */
>  #define X86_FEATURE_ZEN5		( 3*32+ 5) /* CPU based on Zen5 microarchitecture */
>  #define X86_FEATURE_ZEN6		( 3*32+ 6) /* CPU based on Zen6 microarchitecture */
> -/* Free                                 ( 3*32+ 7) */
> +#define X86_FEATURE_RAR			( 3*32+ 7) /* Intel Remote Action Request */
>  #define X86_FEATURE_CONSTANT_TSC	( 3*32+ 8) /* "constant_tsc" TSC ticks at a constant rate */
>  #define X86_FEATURE_UP			( 3*32+ 9) /* "up" SMP kernel running on UP */
>  #define X86_FEATURE_ART			( 3*32+10) /* "art" Always running timer (ART) */
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 8feb8fd2957a..dd662c42f510 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1545,6 +1545,18 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
>  	setup_force_cpu_bug(X86_BUG_L1TF);
>  }
>  
> +static void __init detect_rar(struct cpuinfo_x86 *c)
> +{
> +	u64 msr;
> +
> +	if (cpu_has(c, X86_FEATURE_CORE_CAPABILITIES)) {
> +		rdmsrl(MSR_IA32_CORE_CAPABILITIES, msr);
> +
> +		if (msr & CORE_CAP_RAR)
> +			setup_force_cpu_cap(X86_FEATURE_RAR);
> +	}
> +}
> +
>  /*
>   * The NOPL instruction is supposed to exist on all CPUs of family >= 6;
>   * unfortunately, that's not true in practice because of early VIA
> @@ -1771,6 +1783,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>  		setup_clear_cpu_cap(X86_FEATURE_LA57);
>  
>  	detect_nopl();
> +	detect_rar(c);
>  }

Move all this gunk into early_init_intel().

-- 
Regards/Gruss,
    Boris.

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