diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 6428c8fe3e..10c71132db 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -57,7 +57,7 @@ bool __read_mostly iommu_qinval = true;
 bool __read_mostly iommu_snoop = true;
 #endif
 
-int nr_iommus;
+static unsigned int __initdata nr_iommus;
 
 static struct iommu_ops vtd_ops;
 static struct tasklet vtd_fault_tasklet;
@@ -1165,13 +1165,6 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
     unsigned long sagaw, nr_dom;
     int agaw;
 
-    if ( nr_iommus >= MAX_IOMMUS )
-    {
-        dprintk(XENLOG_ERR VTDPREFIX,
-                "IOMMU: nr_iommus %d > MAX_IOMMUS\n", nr_iommus + 1);
-        return -ENOMEM;
-    }
-
     iommu = xzalloc(struct vtd_iommu);
     if ( iommu == NULL )
         return -ENOMEM;
@@ -2226,6 +2219,10 @@ static void __hwdom_init setup_hwdom_rmrr(struct domain *d)
     pcidevs_unlock();
 }
 
+static struct iommu_state {
+    uint32_t fectl;
+} *__read_mostly iommu_state;
+
 static int __init vtd_setup(void)
 {
     struct acpi_drhd_unit *drhd;
@@ -2251,6 +2248,13 @@ static int __init vtd_setup(void)
         goto error;
     }
 
+    iommu_state = xmalloc_array(struct iommu_state, nr_iommus);
+    if ( !iommu_state )
+    {
+        ret = -ENOMEM;
+        goto error;
+    }
+
     /* We enable the following features only if they are supported by all VT-d
      * engines: Snoop Control, DMA passthrough, Queued Invalidation, Interrupt
      * Remapping, and Posted Interrupt
@@ -2508,8 +2512,6 @@ static int intel_iommu_group_id(u16 seg, u8 bus, u8 devfn)
         return PCI_BDF2(bus, devfn);
 }
 
-static u32 iommu_state[MAX_IOMMUS][MAX_IOMMU_REGS];
-
 static int __must_check vtd_suspend(void)
 {
     struct acpi_drhd_unit *drhd;
@@ -2534,14 +2536,7 @@ static int __must_check vtd_suspend(void)
         iommu = drhd->iommu;
         i = iommu->index;
 
-        iommu_state[i][DMAR_FECTL_REG] =
-            (u32) dmar_readl(iommu->reg, DMAR_FECTL_REG);
-        iommu_state[i][DMAR_FEDATA_REG] =
-            (u32) dmar_readl(iommu->reg, DMAR_FEDATA_REG);
-        iommu_state[i][DMAR_FEADDR_REG] =
-            (u32) dmar_readl(iommu->reg, DMAR_FEADDR_REG);
-        iommu_state[i][DMAR_FEUADDR_REG] =
-            (u32) dmar_readl(iommu->reg, DMAR_FEUADDR_REG);
+        iommu_state[i].fectl = dmar_readl(iommu->reg, DMAR_FECTL_REG);
 
         /* don't disable VT-d engine when force_iommu is set. */
         if ( force_iommu )
@@ -2594,15 +2589,13 @@ static void vtd_resume(void)
     for_each_drhd_unit ( drhd )
     {
         iommu = drhd->iommu;
-        i = iommu->index;
 
         spin_lock_irqsave(&iommu->register_lock, flags);
-        dmar_writel(iommu->reg, DMAR_FEDATA_REG,
-                    iommu_state[i][DMAR_FEDATA_REG]);
-        dmar_writel(iommu->reg, DMAR_FEADDR_REG,
-                    iommu_state[i][DMAR_FEADDR_REG]);
-        dmar_writel(iommu->reg, DMAR_FEUADDR_REG,
-                    iommu_state[i][DMAR_FEUADDR_REG]);
+        dmar_writel(iommu->reg, DMAR_FEDATA_REG, iommu->msi.msg.data);
+        dmar_writel(iommu->reg, DMAR_FEADDR_REG, iommu->msi.msg.address_lo);
+        if ( x2apic_enabled )
+            dmar_writel(iommu->reg, DMAR_FEUADDR_REG,
+                        iommu->msi.msg.address_hi);
         spin_unlock_irqrestore(&iommu->register_lock, flags);
     }
 
@@ -2615,8 +2608,7 @@ static void vtd_resume(void)
         i = iommu->index;
 
         spin_lock_irqsave(&iommu->register_lock, flags);
-        dmar_writel(iommu->reg, DMAR_FECTL_REG,
-                    (u32) iommu_state[i][DMAR_FECTL_REG]);
+        dmar_writel(iommu->reg, DMAR_FECTL_REG, iommu_state[i].fectl);
         spin_unlock_irqrestore(&iommu->register_lock, flags);
 
         iommu_enable_translation(drhd);
diff --git a/xen/drivers/passthrough/vtd/iommu.h b/xen/drivers/passthrough/vtd/iommu.h
index 216791b3d6..6f41068c09 100644
--- a/xen/drivers/passthrough/vtd/iommu.h
+++ b/xen/drivers/passthrough/vtd/iommu.h
@@ -499,8 +499,6 @@ struct qinval_entry {
 #define VTD_PAGE_TABLE_LEVEL_3  3
 #define VTD_PAGE_TABLE_LEVEL_4  4
 
-#define MAX_IOMMU_REGS 0xc0
-
 extern struct list_head acpi_drhd_units;
 extern struct list_head acpi_rmrr_units;
 extern struct list_head acpi_ioapic_units;
diff --git a/xen/include/asm-x86/iommu.h b/xen/include/asm-x86/iommu.h
index 970eb06ffa..65a0b02f60 100644
--- a/xen/include/asm-x86/iommu.h
+++ b/xen/include/asm-x86/iommu.h
@@ -22,7 +22,6 @@
 #include <asm/hvm/vmx/vmcs.h>
 
 #define DEFAULT_DOMAIN_ADDRESS_WIDTH 48
-#define MAX_IOMMUS 32
 
 struct g2m_ioport {
     struct list_head list;