Indirect branch tracking for Intel CPUs

All derivative works of the kernel must be GPLv2 - that's how the GPL works. AFAIK Linus's opinion is that if you only use non-GPL-marked exported functions - functions you might expect to find in any kernel - then your module is not a derivative work of Linux in particular, but GPL exports are functions that are sufficiently entangled with Linux in particular that you can't reasonably claim your driver is not derived from Linux.