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.

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>

diff --git a/tools/xenpaging/xenpaging.c b/tools/xenpaging/xenpaging.c
index 64e265c40539dd333e27c52eb4c8ba5936b7ac9f..d33dde1c87053bf3b4535dee0f6bfa913c37551b 100644 (file)
--- a/tools/xenpaging/xenpaging.c
+++ b/tools/xenpaging/xenpaging.c
@@ -123,7 +123,17 @@ xenpaging_t *xenpaging_init(xc_interface **xch_r, domid_t domain_id)
                              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;
     }
 

diff --git a/xen/arch/x86/mm/mem_event.c b/xen/arch/x86/mm/mem_event.c
index 5bf211d0a8443846fac02fc3ae6979e7ee6c2443..5187a72a6cf08b973c543d672321f8c13c5f54cb 100644 (file)
--- a/xen/arch/x86/mm/mem_event.c
+++ b/xen/arch/x86/mm/mem_event.c
@@ -214,6 +214,13 @@ int mem_event_domctl(struct domain *d, xen_domctl_mem_event_op_t *mec,
             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) &&