diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index 5f164ff..f5a662a 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -491,6 +491,7 @@
 	int map_size;
 	u32 ver;
 	static int iommu_allocated = 0;
+	int agaw;
 
 	iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
 	if (!iommu)
@@ -506,6 +507,15 @@
 	iommu->cap = dmar_readq(iommu->reg + DMAR_CAP_REG);
 	iommu->ecap = dmar_readq(iommu->reg + DMAR_ECAP_REG);
 
+	agaw = iommu_calculate_agaw(iommu);
+	if (agaw < 0) {
+		printk(KERN_ERR
+			"Cannot get a valid agaw for iommu (seq_id = %d)\n",
+			iommu->seq_id);
+		goto error;
+	}
+	iommu->agaw = agaw;
+
 	/* 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));
diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 9dca689..3ecfa23 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -362,6 +362,28 @@
 	kmem_cache_free(iommu_iova_cache, iova);
 }
 
+
+static inline int width_to_agaw(int width);
+
+/* calculate agaw for each iommu.
+ * "SAGAW" may be different across iommus, use a default agaw, and
+ * get a supported less agaw for iommus that don't support the default agaw.
+ */
+int iommu_calculate_agaw(struct intel_iommu *iommu)
+{
+	unsigned long sagaw;
+	int agaw = -1;
+
+	sagaw = cap_sagaw(iommu->cap);
+	for (agaw = width_to_agaw(DEFAULT_DOMAIN_ADDRESS_WIDTH);
+	     agaw >= 0; agaw--) {
+		if (test_bit(agaw, &sagaw))
+			break;
+	}
+
+	return agaw;
+}
+
 /* in native case, each domain is related to only one iommu */
 static struct intel_iommu *domain_get_iommu(struct dmar_domain *domain)
 {
diff --git a/include/linux/dma_remapping.h b/include/linux/dma_remapping.h
index 7799a85..136f170 100644
--- a/include/linux/dma_remapping.h
+++ b/include/linux/dma_remapping.h
@@ -17,6 +17,7 @@
 struct root_entry;
 
 extern void free_dmar_iommu(struct intel_iommu *iommu);
+extern int iommu_calculate_agaw(struct intel_iommu *iommu);
 
 extern int dmar_disabled;
 
diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 1bff7bf..06349fd 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -290,6 +290,7 @@
 	u32		gcmd; /* Holds TE, EAFL. Don't need SRTP, SFL, WBF */
 	spinlock_t	register_lock; /* protect register handling */
 	int		seq_id;	/* sequence id of the iommu */
+	int		agaw; /* agaw of this iommu */
 
 #ifdef CONFIG_DMAR
 	unsigned long 	*domain_ids; /* bitmap of domains */