diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index ff33866..2831442 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -43,10 +43,19 @@
 
 #include "irq_remapping.h"
 
-/* No locks are needed as DMA remapping hardware unit
- * list is constructed at boot time and hotplug of
- * these units are not supported by the architecture.
+/*
+ * Assumptions:
+ * 1) The hotplug framework guarentees that DMAR unit will be hot-added
+ *    before IO devices managed by that unit.
+ * 2) The hotplug framework guarantees that DMAR unit will be hot-removed
+ *    after IO devices managed by that unit.
+ * 3) Hotplug events are rare.
+ *
+ * Locking rules for DMA and interrupt remapping related global data structures:
+ * 1) Use dmar_global_lock in process context
+ * 2) Use RCU in interrupt context
  */
+DECLARE_RWSEM(dmar_global_lock);
 LIST_HEAD(dmar_drhd_units);
 
 struct acpi_table_header * __initdata dmar_tbl;
@@ -565,6 +574,7 @@ static int __init detect_intel_iommu(void)
 {
 	int ret;
 
+	down_write(&dmar_global_lock);
 	ret = dmar_table_detect();
 	if (ret)
 		ret = check_zero_address();
@@ -582,6 +592,7 @@ static int __init detect_intel_iommu(void)
 	}
 	early_acpi_os_unmap_memory((void __iomem *)dmar_tbl, dmar_tbl_size);
 	dmar_tbl = NULL;
+	up_write(&dmar_global_lock);
 
 	return ret ? 1 : -ENODEV;
 }
@@ -1394,10 +1405,12 @@ static int __init dmar_free_unused_resources(void)
 	if (irq_remapping_enabled || intel_iommu_enabled)
 		return 0;
 
+	down_write(&dmar_global_lock);
 	list_for_each_entry_safe(dmaru, dmaru_n, &dmar_drhd_units, list) {
 		list_del(&dmaru->list);
 		dmar_free_drhd(dmaru);
 	}
+	up_write(&dmar_global_lock);
 
 	return 0;
 }
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 7e043ca..25e9b84 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3627,6 +3627,7 @@ static int device_notifier(struct notifier_block *nb,
 	if (!domain)
 		return 0;
 
+	down_read(&dmar_global_lock);
 	if (action == BUS_NOTIFY_UNBOUND_DRIVER && !iommu_pass_through) {
 		domain_remove_one_dev_info(domain, pdev);
 
@@ -3635,6 +3636,7 @@ static int device_notifier(struct notifier_block *nb,
 		    list_empty(&domain->devices))
 			domain_exit(domain);
 	}
+	up_read(&dmar_global_lock);
 
 	return 0;
 }
@@ -3652,6 +3654,7 @@ int __init intel_iommu_init(void)
 	/* VT-d is required for a TXT/tboot launch, so enforce that */
 	force_on = tboot_force_iommu();
 
+	down_write(&dmar_global_lock);
 	if (dmar_table_init()) {
 		if (force_on)
 			panic("tboot: Failed to initialize DMAR table\n");
@@ -3701,6 +3704,7 @@ int __init intel_iommu_init(void)
 		printk(KERN_ERR "IOMMU: dmar init failed\n");
 		goto out_free_reserved_range;
 	}
+	up_write(&dmar_global_lock);
 	printk(KERN_INFO
 	"PCI-DMA: Intel(R) Virtualization Technology for Directed I/O\n");
 
@@ -3726,6 +3730,7 @@ out_free_mempool:
 	iommu_exit_mempool();
 out_free_dmar:
 	intel_iommu_free_dmars();
+	up_write(&dmar_global_lock);
 	return ret;
 }
 
diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
index f307a3f..009a2bb 100644
--- a/drivers/iommu/intel_irq_remapping.c
+++ b/drivers/iommu/intel_irq_remapping.c
@@ -38,6 +38,17 @@ static struct ioapic_scope ir_ioapic[MAX_IO_APICS];
 static struct hpet_scope ir_hpet[MAX_HPET_TBS];
 static int ir_ioapic_num, ir_hpet_num;
 
+/*
+ * Lock ordering:
+ * ->dmar_global_lock
+ *	->irq_2_ir_lock
+ *		->qi->q_lock
+ *	->iommu->register_lock
+ * Note:
+ * intel_irq_remap_ops.{supported,prepare,enable,disable,reenable} are called
+ * in single-threaded environment with interrupt disabled, so no need to tabke
+ * the dmar_global_lock.
+ */
 static DEFINE_RAW_SPINLOCK(irq_2_ir_lock);
 
 static int __init parse_ioapics_under_ir(void);
@@ -312,12 +323,14 @@ static int set_ioapic_sid(struct irte *irte, int apic)
 	if (!irte)
 		return -1;
 
+	down_read(&dmar_global_lock);
 	for (i = 0; i < MAX_IO_APICS; i++) {
 		if (ir_ioapic[i].id == apic) {
 			sid = (ir_ioapic[i].bus << 8) | ir_ioapic[i].devfn;
 			break;
 		}
 	}
+	up_read(&dmar_global_lock);
 
 	if (sid == 0) {
 		pr_warning("Failed to set source-id of IOAPIC (%d)\n", apic);
@@ -337,12 +350,14 @@ static int set_hpet_sid(struct irte *irte, u8 id)
 	if (!irte)
 		return -1;
 
+	down_read(&dmar_global_lock);
 	for (i = 0; i < MAX_HPET_TBS; i++) {
 		if (ir_hpet[i].id == id) {
 			sid = (ir_hpet[i].bus << 8) | ir_hpet[i].devfn;
 			break;
 		}
 	}
+	up_read(&dmar_global_lock);
 
 	if (sid == 0) {
 		pr_warning("Failed to set source-id of HPET block (%d)\n", id);
@@ -799,10 +814,16 @@ static int __init parse_ioapics_under_ir(void)
 
 static int __init ir_dev_scope_init(void)
 {
+	int ret;
+
 	if (!irq_remapping_enabled)
 		return 0;
 
-	return dmar_dev_scope_init();
+	down_write(&dmar_global_lock);
+	ret = dmar_dev_scope_init();
+	up_write(&dmar_global_lock);
+
+	return ret;
 }
 rootfs_initcall(ir_dev_scope_init);
 
@@ -883,23 +904,27 @@ static int intel_setup_ioapic_entry(int irq,
 				    struct io_apic_irq_attr *attr)
 {
 	int ioapic_id = mpc_ioapic_id(attr->ioapic);
-	struct intel_iommu *iommu = map_ioapic_to_ir(ioapic_id);
+	struct intel_iommu *iommu;
 	struct IR_IO_APIC_route_entry *entry;
 	struct irte irte;
 	int index;
 
+	down_read(&dmar_global_lock);
+	iommu = map_ioapic_to_ir(ioapic_id);
 	if (!iommu) {
 		pr_warn("No mapping iommu for ioapic %d\n", ioapic_id);
-		return -ENODEV;
-	}
-
-	entry = (struct IR_IO_APIC_route_entry *)route_entry;
-
-	index = alloc_irte(iommu, irq, 1);
-	if (index < 0) {
-		pr_warn("Failed to allocate IRTE for ioapic %d\n", ioapic_id);
-		return -ENOMEM;
+		index = -ENODEV;
+	} else {
+		index = alloc_irte(iommu, irq, 1);
+		if (index < 0) {
+			pr_warn("Failed to allocate IRTE for ioapic %d\n",
+				ioapic_id);
+			index = -ENOMEM;
+		}
 	}
+	up_read(&dmar_global_lock);
+	if (index < 0)
+		return index;
 
 	prepare_irte(&irte, vector, destination);
 
@@ -918,6 +943,7 @@ static int intel_setup_ioapic_entry(int irq,
 		irte.avail, irte.vector, irte.dest_id,
 		irte.sid, irte.sq, irte.svt);
 
+	entry = (struct IR_IO_APIC_route_entry *)route_entry;
 	memset(entry, 0, sizeof(*entry));
 
 	entry->index2	= (index >> 15) & 0x1;
@@ -1048,20 +1074,23 @@ static int intel_msi_alloc_irq(struct pci_dev *dev, int irq, int nvec)
 	struct intel_iommu *iommu;
 	int index;
 
+	down_read(&dmar_global_lock);
 	iommu = map_dev_to_ir(dev);
 	if (!iommu) {
 		printk(KERN_ERR
 		       "Unable to map PCI %s to iommu\n", pci_name(dev));
-		return -ENOENT;
+		index = -ENOENT;
+	} else {
+		index = alloc_irte(iommu, irq, nvec);
+		if (index < 0) {
+			printk(KERN_ERR
+			       "Unable to allocate %d IRTE for PCI %s\n",
+			       nvec, pci_name(dev));
+			index = -ENOSPC;
+		}
 	}
+	up_read(&dmar_global_lock);
 
-	index = alloc_irte(iommu, irq, nvec);
-	if (index < 0) {
-		printk(KERN_ERR
-		       "Unable to allocate %d IRTE for PCI %s\n", nvec,
-		       pci_name(dev));
-		return -ENOSPC;
-	}
 	return index;
 }
 
@@ -1069,33 +1098,40 @@ static int intel_msi_setup_irq(struct pci_dev *pdev, unsigned int irq,
 			       int index, int sub_handle)
 {
 	struct intel_iommu *iommu;
+	int ret = -ENOENT;
 
+	down_read(&dmar_global_lock);
 	iommu = map_dev_to_ir(pdev);
-	if (!iommu)
-		return -ENOENT;
-	/*
-	 * setup the mapping between the irq and the IRTE
-	 * base index, the sub_handle pointing to the
-	 * appropriate interrupt remap table entry.
-	 */
-	set_irte_irq(irq, iommu, index, sub_handle);
+	if (iommu) {
+		/*
+		 * setup the mapping between the irq and the IRTE
+		 * base index, the sub_handle pointing to the
+		 * appropriate interrupt remap table entry.
+		 */
+		set_irte_irq(irq, iommu, index, sub_handle);
+		ret = 0;
+	}
+	up_read(&dmar_global_lock);
 
-	return 0;
+	return ret;
 }
 
 static int intel_setup_hpet_msi(unsigned int irq, unsigned int id)
 {
-	struct intel_iommu *iommu = map_hpet_to_ir(id);
+	int ret = -1;
+	struct intel_iommu *iommu;
 	int index;
 
-	if (!iommu)
-		return -1;
-
-	index = alloc_irte(iommu, irq, 1);
-	if (index < 0)
-		return -1;
+	down_read(&dmar_global_lock);
+	iommu = map_hpet_to_ir(id);
+	if (iommu) {
+		index = alloc_irte(iommu, irq, 1);
+		if (index >= 0)
+			ret = 0;
+	}
+	up_read(&dmar_global_lock);
 
-	return 0;
+	return ret;
 }
 
 struct irq_remap_ops intel_irq_remap_ops = {
diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index 8aa7561..9572a4f 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -25,6 +25,7 @@
 #include <linux/types.h>
 #include <linux/msi.h>
 #include <linux/irqreturn.h>
+#include <linux/rwsem.h>
 
 struct acpi_dmar_header;
 
@@ -48,6 +49,7 @@ struct dmar_drhd_unit {
 	struct intel_iommu *iommu;
 };
 
+extern struct rw_semaphore dmar_global_lock;
 extern struct list_head dmar_drhd_units;
 
 #define for_each_drhd_unit(drhd) \
