postcopy: ram_enable_notify to switch on userfault

Mark the area of RAM as 'userfault'
Start up a fault-thread to handle any userfaults we might receive
from it (to be filled in later)

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 674f0fb953..a7210a22b4 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1381,6 +1381,15 @@ static int loadvm_postcopy_handle_listen(MigrationIncomingState *mis)
         return -1;
     }
 
+    /*
+     * Sensitise RAM - can now generate requests for blocks that don't exist
+     * However, at this point the CPU shouldn't be running, and the IO
+     * shouldn't be doing anything yet so don't actually expect requests
+     */
+    if (postcopy_ram_enable_notify(mis)) {
+        return -1;
+    }
+
     /* TODO start up the postcopy listening thread */
     return 0;
 }