linux-kernel - Re: [PATCH 2/4] KVM: x86: Advertise AMX CPUIDs in subleaf 0x1E.0x1 to userspace

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Message-ID: <aXO1_kmDSu_H1BoL@google.com>
Date: Fri, 23 Jan 2026 09:55:10 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Zhao Liu <zhao1.liu@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Chao Gao <chao.gao@...el.com>, 
	Xudong Hao <xudong.hao@...el.com>
Subject: Re: [PATCH 2/4] KVM: x86: Advertise AMX CPUIDs in subleaf 0x1E.0x1 to userspace

On Thu, Nov 20, 2025, Zhao Liu wrote:
> diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
> index 743ab25ba787..99ec9e656655 100644
> --- a/arch/x86/kvm/reverse_cpuid.h
> +++ b/arch/x86/kvm/reverse_cpuid.h
> @@ -44,6 +44,16 @@
>  #define KVM_X86_FEATURE_BHI_CTRL	KVM_X86_FEATURE(CPUID_7_2_EDX, 4)
>  #define X86_FEATURE_MCDT_NO		KVM_X86_FEATURE(CPUID_7_2_EDX, 5)
>  
> +/* Intel-defined sub-features, CPUID level 0x0000001E:1 (EAX) */
> +#define X86_FEATURE_AMX_INT8_MIRROR	KVM_X86_FEATURE(CPUID_1E_1_EAX, 0) /* Mirror of X86_FEATURE_AMX_INT8 */
> +#define X86_FEATURE_AMX_BF16_MIRROR	KVM_X86_FEATURE(CPUID_1E_1_EAX, 1) /* Mirror of X86_FEATURE_AMX_BF16 */
> +#define X86_FEATURE_AMX_COMPLEX_MIRROR	KVM_X86_FEATURE(CPUID_1E_1_EAX, 2) /* Mirror of X86_FEATURE_AMX_COMPLEX */
> +#define X86_FEATURE_AMX_FP16_MIRROR	KVM_X86_FEATURE(CPUID_1E_1_EAX, 3) /* Mirror of X86_FEATURE_AMX_FP16 */

Unless someone feels *very* strongly about the "mirror" terminology, I'm going to
use ALIAS instead of MIRROR when applying, to match KVM's existing terminology for
the 8000_0001.EDX => 1.EDX aliases.

/*
 * Intel-defined sub-features, CPUID level 0x0000001E:1 (EAX).  Note, several
 * of the bits are aliases to features of the same name that are enumerated via
 * various CPUID.0x7 sub-leafs.
 */
#define X86_FEATURE_AMX_INT8_ALIAS	KVM_X86_FEATURE(CPUID_1E_1_EAX, 0)
#define X86_FEATURE_AMX_BF16_ALIAS	KVM_X86_FEATURE(CPUID_1E_1_EAX, 1)
#define X86_FEATURE_AMX_COMPLEX_ALIAS	KVM_X86_FEATURE(CPUID_1E_1_EAX, 2)
#define X86_FEATURE_AMX_FP16_ALIAS	KVM_X86_FEATURE(CPUID_1E_1_EAX, 3)