diff -ur xen-4.0.0/xen/drivers/passthrough/iommu.c xen-4.0.0.p6t/xen/drivers/passthrough/iommu.c
--- xen-4.0.0/xen/drivers/passthrough/iommu.c	2010-04-07 18:12:06.000000000 +0200
+++ xen-4.0.0.p6t/xen/drivers/passthrough/iommu.c	2010-04-09 15:45:20.298264009 +0200
@@ -44,7 +44,7 @@
 bool_t __read_mostly force_iommu;
 bool_t __read_mostly iommu_verbose;
 bool_t __read_mostly iommu_workaround_bios_bug;
-bool_t __read_mostly iommu_passthrough;
+bool_t __read_mostly iommu_passthrough = 1;
 bool_t __read_mostly iommu_snoop = 1;
 bool_t __read_mostly iommu_qinval = 1;
 bool_t __read_mostly iommu_intremap = 1;
@@ -71,8 +71,8 @@
             force_iommu = 1;
         else if ( !strcmp(s, "workaround_bios_bug") )
             iommu_workaround_bios_bug = 1;
-        else if ( !strcmp(s, "passthrough") )
-            iommu_passthrough = 1;
+        else if ( !strcmp(s, "no-passthrough") )
+            iommu_passthrough = 0;
         else if ( !strcmp(s, "verbose") )
             iommu_verbose = 1;
         else if ( !strcmp(s, "no-snoop") )
diff -ur xen-4.0.0/xen/drivers/passthrough/vtd/dmar.c xen-4.0.0.p6t/xen/drivers/passthrough/vtd/dmar.c
--- xen-4.0.0/xen/drivers/passthrough/vtd/dmar.c	2010-04-07 18:12:06.000000000 +0200
+++ xen-4.0.0.p6t/xen/drivers/passthrough/vtd/dmar.c	2010-04-09 15:44:25.709650509 +0200
@@ -499,8 +499,7 @@
     {
         dprintk(XENLOG_WARNING VTDPREFIX,
                 "  RMRR address range not in reserved memory "
-                "base = %"PRIx64" end = %"PRIx64"; "
-                "iommu_inclusive_mapping=1 parameter may be needed.\n",
+                "base = %"PRIx64" end = %"PRIx64"\n",
                 base_addr, end_addr);
     }
 #endif
@@ -559,8 +558,7 @@
             dprintk(XENLOG_WARNING VTDPREFIX,
                 "  The RMRR (%"PRIx64", %"PRIx64") is incorrect!\n",
                 rmrru->base_address, rmrru->end_address);
-            xfree(rmrru);
-            ret = -EFAULT;
+            acpi_register_rmrr_unit(rmrru);
         }
         else
         {
diff -ur xen-4.0.0/xen/drivers/passthrough/vtd/x86/vtd.c xen-4.0.0.p6t/xen/drivers/passthrough/vtd/x86/vtd.c
--- xen-4.0.0/xen/drivers/passthrough/vtd/x86/vtd.c	2010-04-07 18:12:06.000000000 +0200
+++ xen-4.0.0.p6t/xen/drivers/passthrough/vtd/x86/vtd.c	2010-04-09 15:44:25.709650509 +0200
@@ -27,13 +27,6 @@
 #include "../dmar.h"
 #include "../vtd.h"

-/*
- * iommu_inclusive_mapping: when set, all memory below 4GB is included in dom0
- * 1:1 iommu mappings except xen and unusable regions.
- */
-static int iommu_inclusive_mapping = 1;
-boolean_param("iommu_inclusive_mapping", iommu_inclusive_mapping);
-
 void *map_vtd_domain_page(u64 maddr)
 {
     return map_domain_page(maddr >> PAGE_SHIFT_4K);
@@ -135,17 +128,6 @@

     for ( i = 0; i < max_pfn; i++ )
     {
-        /*
-         * Set up 1:1 mapping for dom0. Default to use only conventional RAM
-         * areas and let RMRRs include needed reserved regions. When set, the
-         * inclusive mapping maps in everything below 4GB except unusable
-         * ranges.
-         */
-        if ( !page_is_ram_type(i, RAM_TYPE_CONVENTIONAL) &&
-             (!iommu_inclusive_mapping ||
-              page_is_ram_type(i, RAM_TYPE_UNUSABLE)) )
-            continue;
-
         /* Exclude Xen bits */
         if ( xen_in_range(i) )
             continue;