diff -r a9ba2e80765f xen/drivers/passthrough/amd/pci_amd_iommu.c
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c	Tue Feb 01 17:30:54 2011 +0100
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c	Tue Feb 01 17:32:07 2011 +0100
@@ -298,7 +298,7 @@ static int reassign_device( struct domai
     list_move(&pdev->domain_list, &target->arch.pdev_list);
     pdev->domain = target;
 
-    if ( target->max_pages > 0 )
+    if ( target != dom0 && target->max_pages > 0 )
         t->paging_mode = get_paging_mode(target->max_pages);
 
     /* IO page tables might be destroyed after pci-detach the last device