linux-kernel - Re: [PATCH v3 2/2] x86: KVM: Advertise AMD's speculation control features

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Message-ID: <20250411094404.GKZ_jkZC9Zb0Lc_zU-@fat_crate.local>
Date: Fri, 11 Apr 2025 11:44:04 +0200
From: Borislav Petkov <bp@...en8.de>
To: Maksim Davydov <davydov-max@...dex-team.ru>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	babu.moger@....com, seanjc@...gle.com, mingo@...hat.com,
	tglx@...utronix.de, dave.hansen@...ux.intel.com, hpa@...or.com,
	jmattson@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v3 2/2] x86: KVM: Advertise AMD's speculation control
 features

On Wed, Dec 04, 2024 at 04:43:45PM +0300, Maksim Davydov wrote:
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 45f87a026bba..0a709d03ee5c 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -343,7 +343,10 @@
>  #define X86_FEATURE_AMD_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier */
>  #define X86_FEATURE_AMD_IBRS		(13*32+14) /* Indirect Branch Restricted Speculation */
>  #define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors */
> +#define X86_FEATURE_AMD_IBRS_ALWAYS_ON	(13*32+16) /* Indirect Branch Restricted Speculation always-on preferred */
>  #define X86_FEATURE_AMD_STIBP_ALWAYS_ON	(13*32+17) /* Single Thread Indirect Branch Predictors always-on preferred */
> +#define X86_FEATURE_AMD_IBRS_PREFERRED	(13*32+18) /* Indirect Branch Restricted Speculation is preferred over SW solution */
> +#define X86_FEATURE_AMD_IBRS_SAME_MODE	(13*32+19) /* Indirect Branch Restricted Speculation provides Same Mode protection */

This is an AMD-specific leaf - you don't need to put "AMD_" in front of every
bit.

-- 
Regards/Gruss,
    Boris.

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