[Xen-devel] [PATCH 04/16] xenpaging: allow only one xenpaging binary per guest

[Olaf Hering <olaf@xxxxxxxxx>]

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

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
Already-Acked-by: Patrick Colp <pjcolp@xxxxxxxxx>
Already-Acked-by: Keir Fraser <keir.fraser@xxxxxxxxxx>

---
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(-)

--- xen-unstable.hg-4.1.22344.orig/tools/xenpaging/xenpaging.c
+++ xen-unstable.hg-4.1.22344/tools/xenpaging/xenpaging.c
@@ -123,7 +123,17 @@ xenpaging_t *xenpaging_init(xc_interface
                              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:
+                perror("Error initialising shared page");
+                break;
+        }
         goto err;
     }
 
--- xen-unstable.hg-4.1.22344.orig/xen/arch/x86/mm/mem_event.c
+++ xen-unstable.hg-4.1.22344/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 ( !(hap_enabled(d) &&


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