The FSGSBASE
patch series is up to its thirteenth version as of late May. It
enables some “new”
instructions for the x86 architecture, opening the way for a number of
significant performance improvements. One might think that such a patch
series would be a shoe-in, but FSGSBASE has had a troubled history;
meanwhile, the delays in getting it merged may have led to a number of
users installing root holes on their Linux systems in the hope of improving
security.

Source: LWN.net – [$] A possible end to the FSGSBASE saga