diff -r ef86ff3c8514 linux-2.6-xen-sparse/drivers/xen/pciback/conf_space_capability.c
--- a/linux-2.6-xen-sparse/drivers/xen/pciback/conf_space_capability.c	Wed Apr 26 19:40:00 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/pciback/conf_space_capability.c	Thu May  4 10:54:49 2006
@@ -61,11 +61,15 @@
 
 extern struct pciback_config_capability pciback_config_capability_vpd;
 extern struct pciback_config_capability pciback_config_capability_pm;
+extern struct pciback_config_capability pciback_config_capability_msi;
+extern struct pciback_config_capability pciback_config_capability_msx;
 
 int pciback_config_capability_init(void)
 {
 	register_capability(&pciback_config_capability_vpd);
 	register_capability(&pciback_config_capability_pm);
+	register_capability(&pciback_config_capability_msi);
+	register_capability(&pciback_config_capability_msix);
 
 	return 0;
 }
diff -r ef86ff3c8514 linux-2.6-xen-sparse/drivers/xen/pciback/conf_space_capability_msi.c
--- /dev/null	Wed Apr 26 19:40:00 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/pciback/conf_space_capability_msi.c	Thu May  4 10:54:49 2006
@@ -0,0 +1,32 @@
+/*
+ * PCI Backend - Configuration space overlay for Message Signaled Interrupts
+ *
+ * Author: Ryan Wilson <hap9@xxxxxxxxxxxxxx>
+ */
+
+#include <linux/pci.h>
+#include "conf_space.h"
+#include "conf_space_capability.h"
+
+static struct config_field caplist_msi[] = {
+	/* we must protect against writes to the flags field which
+	 * could enable MSI */
+	{
+	 .offset    = PCI_MSI_FLAGS,
+	 .size      = 2,
+	 .u.w.read  = pciback_read_config_word,
+	 },
+	{
+	 .size = 0,
+	 },
+};
+ 
+struct pciback_config_capability pciback_config_capability_msi = {
+	.capability = PCI_CAP_ID_MSI,
+	.fields = caplist_msi,
+};
+
+struct pciback_config_capability pciback_config_capability_msix = {
+	.capability = PCI_CAP_ID_MSIX,
+	.fields = caplist_msi,
+};