/*
+	 * Temporary hack: zero gs now that we've saved it so that Xen
+	 * doesn't try to reload the old value after changing the GDT
+	 * during the context switch.  This can go away once Xen has
+	 * been taught to only reload %gs when it absolutely must.
+	 */
+	loadsegment(gs, 0);

Sorry, but i don't really want that unconditionally in the context switch.
Adding a paravirt ops for it would be also ugly. Can Xen be fixed?

-Andi