Microsoft Hyper-V Guests Get PCID Support With Linux 4.16

With the in-development Linux 4.16 kernel there is now support for PCID with Microsoft Hyper-V virtualization guests.

Up until now support for PCID (Process Context Identifiers) was intentionally disabled for Hyper-V guests with the code never having been tested for how it works on PCID-enabled systems. But Red Hat developers have now determined it's safe to enable and the switch is happening for Linux 4.16.

The timing is notable because Process Context Identifiers have been getting a lot of fanfare recently with PCID support being beneficial to lessening the impact of Kernel Page Table Isolation (KPTI). When PCID support is present for KPTI, the TLB flush can generally be avoided. PCID support has been available since the Intel Westmere days.

So this PCID change for Hyper-V guests should be beneficial for performance reasons to up-to-date Hyper-V guests.