diff -r bbad08b156e9 -r 072ffd2fa8f7 xen/drivers/passthrough/vtd/dmar.c
--- a/xen/drivers/passthrough/vtd/dmar.c	Thu Jan 21 14:08:42 2010 +0900
+++ b/xen/drivers/passthrough/vtd/dmar.c	Thu Jan 21 16:39:46 2010 +0900
@@ -397,7 +397,34 @@
     if ( ret )
         xfree(dmaru);
     else
-        acpi_register_drhd_unit(dmaru);
+    {
+        u8 b, d, f;
+        int i, ignore = 0;
+
+        for ( i = 0; i < dmaru->scope.devices_cnt; i++ )
+        {
+            b = PCI_BUS(dmaru->scope.devices[i]);
+            d = PCI_SLOT(dmaru->scope.devices[i]);
+            f = PCI_FUNC(dmaru->scope.devices[i]);
+
+            if ( pci_device_detect(b, d, f) == 0 )
+            {
+                ignore = 1;
+                break;
+            }
+        }
+
+        if ( ignore )
+        {
+            dprintk(XENLOG_WARNING VTDPREFIX,
+                "  Ignore the DRHD due to "
+                "devices under its scope are not PCI discoverable!\n");
+            xfree(dmaru);
+        }
+        else
+            acpi_register_drhd_unit(dmaru);
+    }
+
     return ret;
 }