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

[Ewan Hai]

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@xxxxxxxxx>
---
 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)
+
 struct cpuid_reg {
 	u32 function;
 	u32 index;
-- 
2.34.1