Advertise the Zhaoxin big-number arithmetic engine to guests via CPUID 0xC0000001 EDX bits 27 (RSA) and 28 (RSA_EN). The RSA feature provides two user-mode instructions for modular arithmetic on big integers, documented in the Zhaoxin PadLock Instruction Reference, chapter 4 ("Modular Multiplication and Exponentiation Engine"). Both support operand sizes from 256 to 32768 bits (in 128-bit increments): - REP XMODEXP (encoding F3 0F A6 F8, subsection 4.1) computes A^B mod M - REP MONTMUL2 (encoding F3 0F A6 F0, subsection 4.2) computes A*B mod M REP MONTMUL2 is the long-mode replacement of legacy REP MONTMUL, which is restricted to compatibility and 32-bit protected modes. These primitives accelerate RSA and related public-key operations. Both instructions are user-mode and available in all CPU modes, with no associated MSR control. The RSA and RSA_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 RSA availability. Signed-off-by: Ewan Hai --- arch/x86/kvm/cpuid.c | 2 ++ arch/x86/kvm/reverse_cpuid.h | 2 ++ 2 files changed, 4 insertions(+) diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 3fb81f7a6107..94ea9abae566 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -1290,6 +1290,8 @@ void kvm_initialize_cpu_caps(void) F(RNG2_EN), F(PHE2), F(PHE2_EN), + F(RSA), + F(RSA_EN), ); /* diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h index f28300c2d5e0..0df96ff9515c 100644 --- a/arch/x86/kvm/reverse_cpuid.h +++ b/arch/x86/kvm/reverse_cpuid.h @@ -85,6 +85,8 @@ #define X86_FEATURE_RNG2_EN KVM_X86_FEATURE(CPUID_C000_0001_EDX, 23) #define X86_FEATURE_PHE2 KVM_X86_FEATURE(CPUID_C000_0001_EDX, 25) #define X86_FEATURE_PHE2_EN KVM_X86_FEATURE(CPUID_C000_0001_EDX, 26) +#define X86_FEATURE_RSA KVM_X86_FEATURE(CPUID_C000_0001_EDX, 27) +#define X86_FEATURE_RSA_EN KVM_X86_FEATURE(CPUID_C000_0001_EDX, 28) struct cpuid_reg { u32 function; -- 2.34.1