The RAPL interface is the sysfs interface utilized in Linux by tools to monitor the power consumption of various power planes (such as package, DRAM, core, etc.).

Until now, it has been impossible to mount this driver in Linux inside a guest using QEMU/KVM because KVM returns 0 for every energy-related register (RAPL MSR).

The aim of this patch is to create a seamless experience for the guest OS and obtain values when attempting to read the affected MSR, thereby enabling the RAPL interface to be mounted inside the guest.

There are two major difficulties to address with this patch:

1. The energy values returned by QEMU/KVM to the guest OS need to be ratioed before being returned. This ratio must be calculated using the CPU time spent by the virtual machine and the host RAPL MSRs.

1. To access the host RAPL MSRs, the virtual machine requires a helper program with the appropriate privileges to access them. Virtual machines should run as privileged users for security reasons.

In terms of business impact, this patch would allow VNF vendors to monitor the consumption of processes (workloads) within their virtual network functions and work on reducing their power consumption.