KVM: x86: Do host CPUID at load time to mask KVM cpu caps

Mask kvm_cpu_caps based on host CPUID in preparation for overriding the
CPUID results during KVM_GET_SUPPORTED_CPUID instead of doing the
masking at runtime.

Note, masking may or may not be necessary, e.g. the kernel rarely, if
ever, sets real CPUID bits that are not supported by hardware.  But, the
code is cheap and only runs once at load, so an abundance of caution is
warranted.

No functional change intended.
Reviewed-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -263,8 +263,16 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
 
 static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
 {
+	const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);
+	struct kvm_cpuid_entry2 entry;
+
 	reverse_cpuid_check(leaf);
 	kvm_cpu_caps[leaf] &= mask;
+
+	cpuid_count(cpuid.function, cpuid.index,
+		    &entry.eax, &entry.ebx, &entry.ecx, &entry.edx);
+
+	kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, &cpuid);
 }
 
 void kvm_set_cpu_caps(void)