Re: [PATCH] KVM: x86/svm: Add module param to control PMU virtualization

[Paolo Bonzini]

On 12/10/21 20:25, Jim Mattson wrote:
> In the long run, I'd like to be able to override this system-wide
> setting on a per-VM basis, for VMs that I trust. (Of course, this
> implies that I trust the userspace process as well.)
>
> How would you feel if we were to add a kvm ioctl to override this
> setting, for a particular VM, guarded by an appropriate permissions
> check, like capable(CAP_SYS_ADMIN) or capable(CAP_SYS_MODULE)?

What's the rationale for guarding this with a capability check?  IIRC 
you don't have such checks for perf_event_open (apart for getting kernel 
addresses, which is not a problem for virtualization).

Paolo