That guard page is absolutely necessary; explain why for
posterity.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/23320cb5017c2da8475ec20fcde8089d82aa2699.1415144745.git.luto@amacapital.netSigned-off-by: Ingo Molnar <mingo@kernel.org>