diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
index 586dd2aa2ca2..78aa1b2af113 100644
--- a/drivers/iommu/dmar.c
+++ b/drivers/iommu/dmar.c
@@ -70,6 +70,7 @@ LIST_HEAD(dmar_drhd_units);
 struct acpi_table_header * __initdata dmar_tbl;
 static acpi_size dmar_tbl_size;
 static int dmar_dev_scope_status = 1;
+static unsigned long dmar_seq_ids[BITS_TO_LONGS(DMAR_UNITS_SUPPORTED)];
 
 static int alloc_iommu(struct dmar_drhd_unit *drhd);
 static void free_iommu(struct intel_iommu *iommu);
@@ -944,11 +945,32 @@ out:
 	return err;
 }
 
+static int dmar_alloc_seq_id(struct intel_iommu *iommu)
+{
+	iommu->seq_id = find_first_zero_bit(dmar_seq_ids,
+					    DMAR_UNITS_SUPPORTED);
+	if (iommu->seq_id >= DMAR_UNITS_SUPPORTED) {
+		iommu->seq_id = -1;
+	} else {
+		set_bit(iommu->seq_id, dmar_seq_ids);
+		sprintf(iommu->name, "dmar%d", iommu->seq_id);
+	}
+
+	return iommu->seq_id;
+}
+
+static void dmar_free_seq_id(struct intel_iommu *iommu)
+{
+	if (iommu->seq_id >= 0) {
+		clear_bit(iommu->seq_id, dmar_seq_ids);
+		iommu->seq_id = -1;
+	}
+}
+
 static int alloc_iommu(struct dmar_drhd_unit *drhd)
 {
 	struct intel_iommu *iommu;
 	u32 ver, sts;
-	static int iommu_allocated = 0;
 	int agaw = 0;
 	int msagaw = 0;
 	int err;
@@ -962,13 +984,16 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	if (!iommu)
 		return -ENOMEM;
 
-	iommu->seq_id = iommu_allocated++;
-	sprintf (iommu->name, "dmar%d", iommu->seq_id);
+	if (dmar_alloc_seq_id(iommu) < 0) {
+		pr_err("IOMMU: failed to allocate seq_id\n");
+		err = -ENOSPC;
+		goto error;
+	}
 
 	err = map_iommu(iommu, drhd->reg_base_addr);
 	if (err) {
 		pr_err("IOMMU: failed to map %s\n", iommu->name);
-		goto error;
+		goto error_free_seq_id;
 	}
 
 	err = -EINVAL;
@@ -1018,9 +1043,11 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 
 	return 0;
 
- err_unmap:
+err_unmap:
 	unmap_iommu(iommu);
- error:
+error_free_seq_id:
+	dmar_free_seq_id(iommu);
+error:
 	kfree(iommu);
 	return err;
 }
@@ -1044,6 +1071,7 @@ static void free_iommu(struct intel_iommu *iommu)
 	if (iommu->reg)
 		unmap_iommu(iommu);
 
+	dmar_free_seq_id(iommu);
 	kfree(iommu);
 }
 
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index b9cc9c2b03fc..2779354321f5 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -330,17 +330,10 @@ static int hw_pass_through = 1;
 /* si_domain contains mulitple devices */
 #define DOMAIN_FLAG_STATIC_IDENTITY	(1 << 1)
 
-/* define the limit of IOMMUs supported in each domain */
-#ifdef	CONFIG_X86
-# define	IOMMU_UNITS_SUPPORTED	MAX_IO_APICS
-#else
-# define	IOMMU_UNITS_SUPPORTED	64
-#endif
-
 struct dmar_domain {
 	int	id;			/* domain id */
 	int	nid;			/* node id */
-	DECLARE_BITMAP(iommu_bmp, IOMMU_UNITS_SUPPORTED);
+	DECLARE_BITMAP(iommu_bmp, DMAR_UNITS_SUPPORTED);
 					/* bitmap of iommus this domain uses*/
 
 	struct list_head devices; 	/* all devices' list */
@@ -2730,12 +2723,12 @@ static int __init init_dmars(void)
 		 * threaded kernel __init code path all other access are read
 		 * only
 		 */
-		if (g_num_of_iommus < IOMMU_UNITS_SUPPORTED) {
+		if (g_num_of_iommus < DMAR_UNITS_SUPPORTED) {
 			g_num_of_iommus++;
 			continue;
 		}
 		printk_once(KERN_ERR "intel-iommu: exceeded %d IOMMUs\n",
-			  IOMMU_UNITS_SUPPORTED);
+			  DMAR_UNITS_SUPPORTED);
 	}
 
 	g_iommus = kcalloc(g_num_of_iommus, sizeof(struct intel_iommu *),
diff --git a/include/linux/dmar.h b/include/linux/dmar.h
index 495df5e48f80..725204fc433e 100644
--- a/include/linux/dmar.h
+++ b/include/linux/dmar.h
@@ -30,6 +30,12 @@
 
 struct acpi_dmar_header;
 
+#ifdef	CONFIG_X86
+# define	DMAR_UNITS_SUPPORTED	MAX_IO_APICS
+#else
+# define	DMAR_UNITS_SUPPORTED	64
+#endif
+
 /* DMAR Flags */
 #define DMAR_INTR_REMAP		0x1
 #define DMAR_X2APIC_OPT_OUT	0x2