On Thu, Feb 19, 2015 at 10:26:09PM +0100, Jiri Kosina wrote: > On Thu, 19 Feb 2015, Josh Poimboeuf wrote: > > > How about with a TIF_IN_USERSPACE thread flag? It could be cleared/set > > right at the border. Then for running tasks it's as simple as: > > > > if (test_tsk_thread_flag(task, TIF_IN_USERSPACE)) > > klp_switch_task_universe(task); > > That's in principle what CONTEXT_TRACKING is doing, i.e. the condition > we'd be interested in would be > > __this_cpu_read(context_tracking.state) == IN_USER > > But it has overhead.
Yeah, that does seem to pretty much do what we want. Unfortunately it has a much higher overhead than just setting a thread flag. And from the Kconfig description for CONTEXT_TRACKING_FORCE, which would enable it on all CPUs during boot, "this option brings an overhead that you don't want in production." Maybe that code needs a rewrite to rely on a thread flag instead. Then we could use it too. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/