KVM: x86: Advertise AVX-NE-CONVERT CPUID to user space

AVX-NE-CONVERT is a new set of instructions which can convert low
precision floating point like BF16/FP16 to high precision floating point
FP32, and can also convert FP32 elements to BF16. This instruction
allows the platform to have improved AI capabilities and better
compatibility.

The bit definition:
CPUID.(EAX=7,ECX=1):EDX[bit 5]

AVX-NE-CONVERT is on a KVM-only subleaf. Plus an x86_FEATURE definition
for this feature bit to direct it to the KVM entry.

Advertise AVX-NE-CONVERT to KVM userspace. This is safe because there
are no new VMX controls or additional host enabling required for guests
to use this feature.

Signed-off-by: Jiaxi Chen <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Jiaxi Chen

arch/x86/kvm/cpuid.c

@@ -668,7 +668,7 @@ void kvm_set_cpu_caps(void)
 	);
 
 	kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX,
-		F(AVX_VNNI_INT8)
+		F(AVX_VNNI_INT8) | F(AVX_NE_CONVERT)
 	);
 
 	kvm_cpu_cap_mask(CPUID_D_1_EAX,

arch/x86/kvm/reverse_cpuid.h

@@ -39,6 +39,7 @@ enum kvm_only_cpuid_leafs {
 
 /* Intel-defined sub-features, CPUID level 0x00000007:1 (EDX) */
 #define X86_FEATURE_AVX_VNNI_INT8       KVM_X86_FEATURE(CPUID_7_1_EDX, 4)
+#define X86_FEATURE_AVX_NE_CONVERT      KVM_X86_FEATURE(CPUID_7_1_EDX, 5)
 
 struct cpuid_reg {
 	u32 function;