* https://lkml.org/lkml/2018/1/4/432 * http://xenbits.xen.org/gitweb/?p=people/andrewcoop/xen.git;a...
It appears that Skylake and later can actually predict retpolines? Some hardware features called IBRS, IBPB, STIBP (not a lot of details on this are out there) are supposedly coming in a microcode update.