http://bugzilla.kernel.org/show_bug.cgi?id=5534

Thanks to Peter Wainwright for isolating the issue.
Thanks to Andi Kleen and Bob Moore for feedback.
Thanks to Richard Mace and others for testing.
Updates by Konstantin Karasyov.
Signed-off-by: Konstantin Karasyov <konstantin.a.karasyov@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>