diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 1e5a10de3471..9ab6ebf46f7a 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -570,14 +570,89 @@ int __init detect_intel_iommu(void)
 }
 
 
+static void unmap_iommu(struct intel_iommu *iommu)
+{
+	iounmap(iommu->reg);
+	release_mem_region(iommu->reg_phys, iommu->reg_size);
+}
+
+/**
+ * map_iommu: map the iommu's registers
+ * @iommu: the iommu to map
+ * @phys_addr: the physical address of the base resgister
+ * 
+ * Memory map the iommu's registers.  Start w/ a single page, and
+ * possibly expand if that turns out to be insufficent.  
+ */
+static int map_iommu(struct intel_iommu *iommu, u64 phys_addr)
+{
+	int map_size, err=0;
+
+	iommu->reg_phys = phys_addr;
+	iommu->reg_size = VTD_PAGE_SIZE;
+
+	if (!request_mem_region(iommu->reg_phys, iommu->reg_size, iommu->name)) {
+		pr_err("IOMMU: can't reserve memory\n");
+		err = -EBUSY;
+		goto out;
+	}
+
+	iommu->reg = ioremap(iommu->reg_phys, iommu->reg_size);
+	if (!iommu->reg) {
+		pr_err("IOMMU: can't map the region\n");
+		err = -ENOMEM;
+		goto release;
+	}
+
+	iommu->cap = dmar_readq(iommu->reg + DMAR_CAP_REG);
+	iommu->ecap = dmar_readq(iommu->reg + DMAR_ECAP_REG);
+
+	if (iommu->cap == (uint64_t)-1 && iommu->ecap == (uint64_t)-1) {
+		err = -EINVAL;
+		warn_invalid_dmar(phys_addr, " returns all ones");
+		goto unmap;
+	}
+
+	/* the registers might be more than one page */
+	map_size = max_t(int, ecap_max_iotlb_offset(iommu->ecap),
+			 cap_max_fault_reg_offset(iommu->cap));
+	map_size = VTD_PAGE_ALIGN(map_size);
+	if (map_size > iommu->reg_size) {
+		iounmap(iommu->reg);
+		release_mem_region(iommu->reg_phys, iommu->reg_size);
+		iommu->reg_size = map_size;
+		if (!request_mem_region(iommu->reg_phys, iommu->reg_size,
+					iommu->name)) {
+			pr_err("IOMMU: can't reserve memory\n");
+			err = -EBUSY;
+			goto out;
+		}
+		iommu->reg = ioremap(iommu->reg_phys, iommu->reg_size);
+		if (!iommu->reg) {
+			pr_err("IOMMU: can't map the region\n");
+			err = -ENOMEM;
+			goto release;
+		}
+	}
+	err = 0;
+	goto out;
+
+unmap:
+	iounmap(iommu->reg);
+release:
+	release_mem_region(iommu->reg_phys, iommu->reg_size);
+out:
+	return err;
+}
+
 int alloc_iommu(struct dmar_drhd_unit *drhd)
 {
 	struct intel_iommu *iommu;
-	int map_size;
 	u32 ver;
 	static int iommu_allocated = 0;
 	int agaw = 0;
 	int msagaw = 0;
+	int err;
 
 	if (!drhd->reg_base_addr) {
 		warn_invalid_dmar(0, "");
@@ -591,19 +666,13 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
 	iommu->seq_id = iommu_allocated++;
 	sprintf (iommu->name, "dmar%d", iommu->seq_id);
 
-	iommu->reg = ioremap(drhd->reg_base_addr, VTD_PAGE_SIZE);
-	if (!iommu->reg) {
-		pr_err("IOMMU: can't map the region\n");
+	err = map_iommu(iommu, drhd->reg_base_addr);
+	if (err) {
+		pr_err("IOMMU: failed to map %s\n", iommu->name);
 		goto error;
 	}
-	iommu->cap = dmar_readq(iommu->reg + DMAR_CAP_REG);
-	iommu->ecap = dmar_readq(iommu->reg + DMAR_ECAP_REG);
-
-	if (iommu->cap == (uint64_t)-1 && iommu->ecap == (uint64_t)-1) {
-		warn_invalid_dmar(drhd->reg_base_addr, " returns all ones");
-		goto err_unmap;
-	}
 
+	err = -EINVAL;
 	agaw = iommu_calculate_agaw(iommu);
 	if (agaw < 0) {
 		pr_err("Cannot get a valid agaw for iommu (seq_id = %d)\n",
@@ -621,19 +690,6 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
 
 	iommu->node = -1;
 
-	/* the registers might be more than one page */
-	map_size = max_t(int, ecap_max_iotlb_offset(iommu->ecap),
-		cap_max_fault_reg_offset(iommu->cap));
-	map_size = VTD_PAGE_ALIGN(map_size);
-	if (map_size > VTD_PAGE_SIZE) {
-		iounmap(iommu->reg);
-		iommu->reg = ioremap(drhd->reg_base_addr, map_size);
-		if (!iommu->reg) {
-			pr_err("IOMMU: can't map the region\n");
-			goto error;
-		}
-	}
-
 	ver = readl(iommu->reg + DMAR_VER_REG);
 	pr_info("IOMMU %d: reg_base_addr %llx ver %d:%d cap %llx ecap %llx\n",
 		iommu->seq_id,
@@ -648,10 +704,10 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
 	return 0;
 
  err_unmap:
-	iounmap(iommu->reg);
+	unmap_iommu(iommu);
  error:
 	kfree(iommu);
-	return -1;
+	return err;
 }
 
 void free_iommu(struct intel_iommu *iommu)
@@ -662,7 +718,8 @@ void free_iommu(struct intel_iommu *iommu)
 	free_dmar_iommu(iommu);
 
 	if (iommu->reg)
-		iounmap(iommu->reg);
+		unmap_iommu(iommu);
+
 	kfree(iommu);
 }
 
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index e6ca56de9936..78e2ada50cd5 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -308,6 +308,8 @@ enum {
 
 struct intel_iommu {
 	void __iomem	*reg; /* Pointer to hardware regs, virtual addr */
+	u64 		reg_phys; /* physical address of hw register set */
+	u64		reg_size; /* size of hw register set */
 	u64		cap;
 	u64		ecap;
 	u32		gcmd; /* Holds TE, EAFL. Don't need SRTP, SFL, WBF */