Linux 5.5 To Advertise RDPRU Support For AMD Zen 2 CPUs Via /proc/cpuinfo

RDPRU is one of the new instruction set extensions of AMD "Zen 2" CPUs that is for reading a processor register that is typically limited to privilege level zero. RDPRU allows for reading select registers at any privilege level. With Linux 5.5, the RDPRU presence will be advertised by the CPU features.

It's still up to user-space for making use of RDPRU, but for software checking from /proc/cpuinfo to see the availability of RDPRU as a supported CPU feature, Linux 5.5 is finally set to advertise it for the Zen 2 CPUs with the Ryzen 3000 series and AMD EPYC 7002 series.

Queued now as part of the x86/cpu changes building up for the Linux 5.5 cycle is the AMD detection for this instruction. The instruction can, of course, be used on earlier kernels this is just about cleanly advertising it through the common cpuinfo area.

This is the only kernel activity around RDPRU besides a KVM change from September for intercepting the RDPRU instruction.