Index: sys/dev/iommu/busdma_iommu.c
===================================================================
--- sys/dev/iommu/busdma_iommu.c
+++ sys/dev/iommu/busdma_iommu.c
@@ -1068,3 +1068,19 @@
 	free(ma, M_TEMP);
 	return (error);
 }
+
+void
+iommu_domain_init(struct iommu_domain *domain)
+{
+
+	RB_INIT(&domain->rb_root);
+	TAILQ_INIT(&domain->unload_entries);
+	mtx_init(&domain->lock, "iodom", NULL, MTX_DEF);
+}
+
+void
+iommu_domain_fini(struct iommu_domain *domain)
+{
+
+	mtx_destroy(&domain->lock);
+}
Index: sys/dev/iommu/iommu.h
===================================================================
--- sys/dev/iommu/iommu.h
+++ sys/dev/iommu/iommu.h
@@ -223,6 +223,8 @@
 
 void iommu_set_buswide_ctx(struct iommu_unit *unit, u_int busno);
 bool iommu_is_buswide_ctx(struct iommu_unit *unit, u_int busno);
+void iommu_domain_init(struct iommu_domain *domain);
+void iommu_domain_fini(struct iommu_domain *domain);
 
 bool bus_dma_iommu_set_buswide(device_t dev);
 int bus_dma_iommu_load_ident(bus_dma_tag_t dmat, bus_dmamap_t map,
Index: sys/x86/iommu/intel_ctx.c
===================================================================
--- sys/x86/iommu/intel_ctx.c
+++ sys/x86/iommu/intel_ctx.c
@@ -332,11 +332,10 @@
 	iodom = DOM2IODOM(domain);
 	domain->domain = id;
 	LIST_INIT(&domain->contexts);
-	RB_INIT(&domain->iodom.rb_root);
-	TAILQ_INIT(&domain->iodom.unload_entries);
 	TASK_INIT(&domain->iodom.unload_task, 0, dmar_domain_unload_task,
 	    domain);
-	mtx_init(&domain->iodom.lock, "dmardom", NULL, MTX_DEF);
+	iommu_domain_init(iodom);
+
 	domain->dmar = dmar;
 	domain->iodom.iommu = &dmar->iommu;
 	domain_pgtbl_init(domain);
@@ -430,8 +429,11 @@
 static void
 dmar_domain_destroy(struct dmar_domain *domain)
 {
+	struct iommu_domain *iodom;
 	struct dmar_unit *dmar;
 
+	iodom = DOM2IODOM(domain);
+
 	KASSERT(TAILQ_EMPTY(&domain->iodom.unload_entries),
 	    ("unfinished unloads %p", domain));
 	KASSERT(LIST_EMPTY(&domain->contexts),
@@ -442,7 +444,7 @@
 	    ("destroying dom %p with refs %d", domain, domain->refs));
 	if ((domain->iodom.flags & IOMMU_DOMAIN_GAS_INITED) != 0) {
 		DMAR_DOMAIN_LOCK(domain);
-		iommu_gas_fini_domain(DOM2IODOM(domain));
+		iommu_gas_fini_domain(iodom);
 		DMAR_DOMAIN_UNLOCK(domain);
 	}
 	if ((domain->iodom.flags & IOMMU_DOMAIN_PGTBL_INITED) != 0) {
@@ -450,7 +452,7 @@
 			DMAR_DOMAIN_PGLOCK(domain);
 		domain_free_pgtbl(domain);
 	}
-	mtx_destroy(&domain->iodom.lock);
+	iommu_domain_fini(iodom);
 	dmar = DOM2DMAR(domain);
 	free_unr(dmar->domids, domain->domain);
 	free(domain, M_DMAR_DOMAIN);