diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 167f533..2ee7060 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -582,6 +582,9 @@
 
 	offset = nr_present = 0;
 
+	/* direct kvm_mmu_page can not be unsync. */
+	BUG_ON(sp->role.direct);
+
 	if (PTTYPE == 32)
 		offset = sp->role.quadrant << PT64_LEVEL_BITS;