There has been a critical design vulnerability in all Intel processors, which has recently caused all long-term Linux versions to apply the KPTI (formerly called KAISER) patch. It would fix such bug by totally separate kernel and user-mode pages, causing compilation performance to suffer from up to 30% penalty. The patch was applied to 4.14.11, 4.9.74 and 4.4.109. We should stabilize 4.9.74 and 4.4.109 and even mask those beforehand to ensure security of our systems.
That would seem premature as 4.4.109 and 4.9.74 do not contain the necessary patches. They are accumulating in queue-4.4 and queue-4.9 at the time of writing.
*** This bug has been marked as a duplicate of bug 643352 ***