The regression was caused by:

commit ca37e57bbe0cf1455ea3e84eb89ed04a132d59e1 (refs/bisect/bad)
Author: Andy Lutomirski <luto@kernel.org>
Date:   Wed Nov 22 20:39:16 2017 -0800

    x86/entry/64: Add missing irqflags tracing to native_load_gs_index()

I'm not sure what commit fixed it off hand.