KVM: x86: Inject #GP if guest attempts to set unsupported EFER bits

EFER.LME and EFER.NX are considered reserved if their respective feature
bits are not advertised to the guest.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -1266,6 +1266,13 @@ static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
 	if (efer & EFER_SVME && !guest_cpuid_has(vcpu, X86_FEATURE_SVM))
 		return false;
 
+	if (efer & (EFER_LME | EFER_LMA) &&
+	    !guest_cpuid_has(vcpu, X86_FEATURE_LM))
+		return false;
+
+	if (efer & EFER_NX && !guest_cpuid_has(vcpu, X86_FEATURE_NX))
+		return false;
+
 	return true;
 
 }