tools/power x86_energy_perf_policy: Input/output error in a VM

tools/power x86_energy_perf_policy: Input/output error in a VM

I've encountered an issue with x86_energy_perf_policy. If I run it on a
machine that I'm told is a qemu-kvm virtual machine running inside a
privileged container, I get the following error:

x86_energy_perf_policy: /dev/cpu/0/msr offset 0x1ad read failed: Input/output error

I get the same error in a Digital Ocean droplet, so that might be a
similar environment.

I created the following patch which is intended to give a more
user-friendly message. It's based on a patch for turbostat from Prarit
Bhargava that was posted some time ago. The patch is "[v2] turbostat:
Running on virtual machine is not supported" [1].

Given my limited knowledge of the topic, I can't say with confidence
that this is the right solution, though (that's why this is not an
official patch submission). Also, I'm not sure what the convention with
exit codes is in this tool. Also, instead of the error message, perhaps
the tool should just not print anything in this case, which is how it
behaves in a "regular" VM?

[1] https://patchwork.kernel.org/patch/9868587/

Signed-off-by: Ondřej Lysoněk <olysonek@redhat.com>
Signed-off-by: Len Brown <len.brown@intel.com>