rcu: provide rcu_virt_note_context_switch() function.

Provide rcu_virt_note_context_switch() for vitalization use to note
quiescent state during guest entry.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 30ebd7c..52b3e02 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -100,6 +100,14 @@
 }
 
 /*
+ * Take advantage of the fact that there is only one CPU, which
+ * allows us to ignore virtualization-based context switches.
+ */
+static inline void rcu_virt_note_context_switch(int cpu)
+{
+}
+
+/*
  * Return the number of grace periods.
  */
 static inline long rcu_batches_completed(void)