Re: [PATCH 1/5] KVM: x86: Expose Zhaoxin SM2 CPUID feature

[Binbin Wu <binbin.wu@linux.intel.com>]

On 5/13/2026 5:36 PM, Ewan Hai wrote:
> Advertise the Zhaoxin SM2 instruction support to guests via CPUID
> 0xC0000001 EDX bits 0 (SM2) and 1 (SM2_EN).
> 
> The SM2 instruction (encoding F2 0F A6 C0) implements the SM2
> elliptic-curve public-key cryptography algorithm specified in
> GM/T 0003-2012; the hardware-level behavior is documented in the
> Zhaoxin GMI Instruction Set Reference, chapter 1 ("SM2"). The
> instruction multiplexes its sub-functions on the RDX[5:0] control
> word: encryption (subsection 1.1), decryption (1.2), signing (1.3),
> signature verification (1.4), the three key-exchange sub-operations
> of section 1.5 (1.5.1 SM2 key-pair generation, which the spec also
> uses for the initiator's ephemeral key; 1.5.2 responder shared-key
> derivation; 1.5.3 initiator shared-key derivation), and two
> preprocess steps for identity and message hashing (1.6.1 and 1.6.2).
> 
> The instruction is user-mode and available in all CPU modes, with no
> associated MSR control. The SM2 and SM2_EN bits are redundant by
> hardware design (set or cleared together) and both serve purely as
> CPUID-level feature-presence reporting flags requiring no KVM
> emulation. Both bits are advertised because different software may
> probe either one when checking for SM2 availability.
> 
> Signed-off-by: Ewan Hai <ewandevelop@gmail.com>
> ---
>  arch/x86/kvm/cpuid.c         | 2 ++
>  arch/x86/kvm/reverse_cpuid.h | 4 ++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index e69156b54cff..1eb4b88aaa80 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1272,6 +1272,8 @@ void kvm_initialize_cpu_caps(void)
>  		kvm_cpu_cap_set(X86_FEATURE_NULL_SEL_CLR_BASE);
>  
>  	kvm_cpu_cap_init(CPUID_C000_0001_EDX,
> +		F(SM2),
> +		F(SM2_EN),
>  		F(XSTORE),
>  		F(XSTORE_EN),
>  		F(XCRYPT),
> diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
> index 657f5f743ed9..7b55110cc046 100644
> --- a/arch/x86/kvm/reverse_cpuid.h
> +++ b/arch/x86/kvm/reverse_cpuid.h
> @@ -76,6 +76,10 @@
>  #define KVM_X86_FEATURE_TSA_SQ_NO	KVM_X86_FEATURE(CPUID_8000_0021_ECX, 1)
>  #define KVM_X86_FEATURE_TSA_L1_NO	KVM_X86_FEATURE(CPUID_8000_0021_ECX, 2)
>  
> +/* Zhaoxin/Centaur sub-features, CPUID level 0xC0000001 (EDX) */
> +#define X86_FEATURE_SM2			KVM_X86_FEATURE(CPUID_C000_0001_EDX, 0)
> +#define X86_FEATURE_SM2_EN		KVM_X86_FEATURE(CPUID_C000_0001_EDX, 1)

Are these new bits really KVM-only feature bits?

KVM_X86_FEATURE() is used for the features either scattered by cpufeatures.h
or features that are 100% KVM-only.

Kernel already has a feature word CPUID_C000_0001_EDX defined for
CPUID 0xC0000001 (EDX). I think these new feature bits should be put together
with the existing ones (i.e. X86_FEATURE_XSTORE, ..., X86_FEATURE_PMM_EN) in
cpufeatures.h.

Same for the other patches.


> +
>  struct cpuid_reg {
>  	u32 function;
>  	u32 index;