xen/xenpaging.xenpaging_init.patch

Subject: xenpaging: allow only one xenpaging binary per guest

Make sure only one xenpaging binary is active per domain.
Print info when the host lacks the required features for xenpaging.

(xen-unstable changeset:   22436:b153d3b71504)
(xen-unstable changeset:   22511:fdf95845c2f8)

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Already-Acked-by: Patrick Colp <pjcolp@cs.ubc.ca>
Already-Acked-by: Keir Fraser <keir.fraser@citrix.com>

---
v2: use perror for default case

 tools/xenpaging/xenpaging.c |   12 +++++++++++-
 xen/arch/x86/mm/mem_event.c |    7 +++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

Index: xen-4.0.2-testing/tools/xenpaging/xenpaging.c
===================================================================
--- xen-4.0.2-testing.orig/tools/xenpaging/xenpaging.c
+++ xen-4.0.2-testing/tools/xenpaging/xenpaging.c
@@ -120,7 +120,17 @@ xenpaging_t *xenpaging_init(domid_t doma
                              paging->mem_event.ring_page);
     if ( rc != 0 )
     {
-        ERROR("Error initialising shared page");
+        switch ( errno ) {
+            case EBUSY:
+                ERROR("xenpaging is (or was) active on this domain");
+                break;
+            case ENODEV:
+                ERROR("EPT not supported for this guest");
+                break;
+            default:
+                ERROR("Error initialising shared page: %s", strerror(errno));
+                break;
+        }
         goto err;
     }
 
Index: xen-4.0.2-testing/xen/arch/x86/mm/mem_event.c
===================================================================
--- xen-4.0.2-testing.orig/xen/arch/x86/mm/mem_event.c
+++ xen-4.0.2-testing/xen/arch/x86/mm/mem_event.c
@@ -214,6 +214,13 @@ int mem_event_domctl(struct domain *d, x
             mfn_t ring_mfn;
             mfn_t shared_mfn;
 
+            /* Only one xenpaging at a time. If xenpaging crashed,
+             * the cache is in an undefined state and so is the guest
+             */
+            rc = -EBUSY;
+            if ( d->mem_event.ring_page )
+                break;
+
             /* Currently only EPT is supported */
             rc = -ENODEV;
             if ( !(is_hvm_domain(d) && d->arch.hvm_domain.hap_enabled &&