KVM: Don't allow the guest to turn off the cpu cache

The cpu cache is a host resource; the guest should not be able to turn
it off (even for itself).

Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/svm.c

@@ -737,8 +737,10 @@ static void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	}
 #endif
 	vcpu->svm->cr0 = cr0;
-	vcpu->svm->vmcb->save.cr0 = cr0 | CR0_PG_MASK | CR0_WP_MASK;
 	vcpu->cr0 = cr0;
+	cr0 |= CR0_PG_MASK | CR0_WP_MASK;
+	cr0 &= ~(CR0_CD_MASK | CR0_NW_MASK);
+	vcpu->svm->vmcb->save.cr0 = cr0;
 }
 
 static void svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)