diff -r e265055ce11c xen/drivers/passthrough/vtd/iommu.c
--- a/xen/drivers/passthrough/vtd/iommu.c       Thu Jan 22 14:05:23 2009 -0500
+++ b/xen/drivers/passthrough/vtd/iommu.c       Wed Feb 04 05:47:08 2009 -0500
@@ -1039,6 +1039,7 @@

     ASSERT(spin_is_locked(&pcidevs_lock));
     spin_lock(&iommu->lock);
+    gdprintk(XENLOG_INFO VTDPREFIX, "domain_context_mapping_one: 1\n");
     maddr = bus_to_context_maddr(iommu, bus);
     context_entries = (struct context_entry *)map_vtd_domain_page(maddr);
     context = &context_entries[devfn];
@@ -1054,6 +1055,7 @@
             res = -EINVAL;
         unmap_vtd_domain_page(context_entries);
         spin_unlock(&iommu->lock);
+        gdprintk(XENLOG_INFO VTDPREFIX, "domain_context_mapping_one: 2\n");
         return res;
     }

@@ -1066,6 +1068,7 @@
     else
     {
         spin_lock(&hd->mapping_lock);
+        gdprintk(XENLOG_INFO VTDPREFIX, "domain_context_mapping_one: 3\n");

         /* Ensure we have pagetables allocated down to leaf PTE. */
         if ( hd->pgd_maddr == 0 )
@@ -1077,6 +1080,7 @@
                 spin_unlock(&hd->mapping_lock);
                 spin_unlock(&iommu->lock);
                 unmap_vtd_domain_page(context_entries);
+                gdprintk(XENLOG_INFO VTDPREFIX, "domain_context_mapping_one: 4\n");
                 return -ENOMEM;
             }
         }
@@ -1120,6 +1124,7 @@
     set_bit(iommu->index, &hd->iommu_bitmap);

     unmap_vtd_domain_page(context_entries);
+    gdprintk(XENLOG_INFO VTDPREFIX, "domain_context_mapping_one: 5\n");

     return 0;
 }
@@ -1268,12 +1273,16 @@
             secdevfn = devfn;
             devfn = bus2bridge[bus].devfn;
             bus = bus2bridge[bus].bus;
+            gdprintk(XENLOG_INFO VTDPREFIX,
+                     "domain_context_mapping:bus2bridge: bdf = %x:%x.%x\n",
+                      bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
             ret = domain_context_mapping_one(domain, drhd->iommu, bus, devfn);
             if ( ret )
                 return ret;
         }

         if ( (secbus != bus) && (secdevfn != 0) )
+        {
             /*
              * The source-id for transactions on non-PCIe buses seem
              * to originate from devfn=0 on the secondary bus behind
@@ -1281,7 +1290,11 @@
              * these scanarios is not particularly well documented
              * anywhere.
              */
+            gdprintk(XENLOG_INFO VTDPREFIX,
+                     "domain_context_mapping:secbus: bdf = %x:%x.%x\n",
+                      secbus, 0, 0);
             ret = domain_context_mapping_one(domain, drhd->iommu, secbus, 0);
+        }
         break;

     default: