AMD Prepping PCID/INVPCID Support For KVM Guests On Zen 3 EPYC

The latest Linux kernel patch work we are seeing out of AMD in preparations for Zen 3 processors coming later this year is INVPCID instruction support for KVM virtualization guests.

One of the new capabilities we are looking forward to on the Zen 3 instruction set side is adding Process Context Identifiers (PCID) support. As part of the PCID support is the INVPCID instruction for Invalidate Process-Context Identifier to invalidate TLB mappings and caches based on the process context identifier.

Sent out on Thursday were 3 patches in allowing INVPCID to be supported by AMD guests for the Kernel-based Virtual Machine (KVM). This allows PCID/INVPCID to be supported by AMD guests on future Zen 3 CPUs, namely next-generation EPYC, and important for performance in the cloud.

Given the timing of these patches, the PCID/INVPCID support for AMD KVM guests won't be merged for the current Linux 5.8 merge window but will have to wait now until at least 5.9. But at least we are seeing more AMD Linux kernel patches coming out now ahead of launch rather than after the product launch. The turnaround time for new Zen 3 features to the Linux kernel so far is shaping up better than Zen / Zen 2 while there still is room for improvement especially with Intel tending to send out their hardware enablement patches to Linux much earlier.