reset runstate_guest handles on soft reset

runstate_guest handles need to be reset to prevent update_runstate_area()
corrupting guest's memory after we resume the guest.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

xen/common/domain.c

@@ -1074,7 +1074,10 @@ int domain_soft_reset(struct domain *d)
     grant_table_warn_active_grants(d);
 
     for_each_vcpu ( d, v )
+    {
+        set_xen_guest_handle(runstate_guest(v), NULL);
         unmap_vcpu_info(v);
+    }
 
     rc = arch_domain_soft_reset(d);
     if ( !rc )