Meltdown mitigations do not flush the TLB when changing from kernel to/from user when the PCID feature is in place. That's basically everywhere from Haswell on

Meltdown mitigations do not flush the TLB when changing from kernel to/from user when the PCID feature is in place. That's basically everywhere from Haswell on (for Linux and Windows), and in some places as early as Nehalem (>= 4.9 kernels on Linux, not Windows).