KVM: nSVM: Check that MBZ bits in CR3 and CR4 are not set on vmrun of nested guests

According to section "Canonicalization and Consistency Checks" in APM vol. 2
the following guest state is illegal:

    "Any MBZ bit of CR3 is set."
    "Any MBZ bit of CR4 is set."

Suggeted-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Message-Id: <1594168797-29444-3-git-send-email-krish.sadhukhan@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 549b3f7..475456a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -955,7 +955,7 @@ int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 }
 EXPORT_SYMBOL_GPL(kvm_set_xcr);
 
-static int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
 	if (cr4 & cr4_reserved_bits)
 		return -EINVAL;
@@ -965,6 +965,7 @@ static int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(kvm_valid_cr4);
 
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {