kvm: set new alias directly when old one is not valid

index db8d7fe..6120e33 100644
@@ -2474,6 +2474,9 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
 
 	/* invalidate any gfn reference in case of deletion/shrinking */
 	memcpy(aliases, kvm->arch.aliases, sizeof(struct kvm_mem_aliases));
+	if (!aliases->aliases[alias->slot].npages)
+		goto set_new_alias;
+
 	aliases->aliases[alias->slot].flags |= KVM_ALIAS_INVALID;
 	old_aliases = kvm->arch.aliases;
 	rcu_assign_pointer(kvm->arch.aliases, aliases);

@@ -2481,6 +2484,8 @@ static int kvm_vm_ioctl_set_memory_alias(struct kvm *kvm,
 	kvm_mmu_zap_all(kvm);
 
 	aliases = old_aliases;
+
+set_new_alias:
 	p = &aliases->aliases[alias->slot];
 	p->base_gfn = alias->guest_phys_addr >> PAGE_SHIFT;
 	p->npages = alias->memory_size >> PAGE_SHIFT;