diff -r 0901aec1d00b xen/drivers/passthrough/vtd/dmar.h
--- a/xen/drivers/passthrough/vtd/dmar.h	Wed Mar 19 00:01:25 2008 +0000
+++ b/xen/drivers/passthrough/vtd/dmar.h	Wed Mar 19 09:16:18 2008 +0800
@@ -100,5 +100,6 @@ struct acpi_rmrr_unit * acpi_find_matche
 
 int vtd_hw_check(void);
 void disable_pmr(struct iommu *iommu);
+int is_usb_device(struct pci_dev *pdev);
 
 #endif // _DMAR_H_
diff -r 0901aec1d00b xen/drivers/passthrough/vtd/iommu.c
--- a/xen/drivers/passthrough/vtd/iommu.c	Wed Mar 19 00:01:25 2008 +0000
+++ b/xen/drivers/passthrough/vtd/iommu.c	Wed Mar 19 09:29:07 2008 +0800
@@ -2019,6 +2019,12 @@ int intel_iommu_assign_device(struct dom
     for_each_rmrr_device( rmrr, pdev )
         if ( pdev->bus == bus && pdev->devfn == devfn )
         {
+            /* FIXME: Because USB RMRR conflicts with guest bios region,
+             * ignore USB RMRR temporarily.
+             */
+            if ( is_usb_device(pdev) )
+                return 0;
+
             ret = iommu_prepare_rmrr_dev(d, rmrr, pdev);
             if ( ret )
             {
diff -r 0901aec1d00b xen/drivers/passthrough/vtd/utils.c
--- a/xen/drivers/passthrough/vtd/utils.c	Wed Mar 19 00:01:25 2008 +0000
+++ b/xen/drivers/passthrough/vtd/utils.c	Wed Mar 19 09:16:18 2008 +0800
@@ -29,6 +29,20 @@
 #define INTEL   0x8086
 #define SEABURG 0x4000
 #define C_STEP  2
+
+int is_usb_device(struct pci_dev *pdev)
+{
+    u8 bus = pdev->bus;
+    u8 dev = PCI_SLOT(pdev->devfn);
+    u8 func = PCI_FUNC(pdev->devfn);
+
+    u16 class = read_pci_config_16(bus, dev, func, PCI_CLASS_DEVICE);
+
+    if ( class == 0xc03 )
+        return 1;
+    else
+        return 0;
+}
 
 int vtd_hw_check(void)
 {