On Fri, Sep 29, 2023 at 03:46:55PM +0000, Sean Christopherson wrote: > > I will firmly reject anything that takes the PMU away from the host > > entirely through. > > Why? What is so wrong with supporting use cases where the platform owner *wants* > to give up host PMU and NMI watchdog functionality? If disabling host PMU usage > were complex, highly invasive, and/or difficult to maintain, then I can understand > the pushback. Because it sucks. You're forcing people to choose between no host PMU or a slow guest PMU. And that's simply not a sane choice for most people -- worse it's not a choice based in technical reality. It's a choice out of lazyness, disabling host PMU is not a requirement for pass-through. Like I wrote, all we need to do is ensure vCPU tasks will never have a perf-event scheduled that covers guest mode. Currently this would be achievable by having event creation for both: - CPU events without attr::exclude_guest=1, and - task events for vCPU task of interest without attr::exclude_guest=1 error with -EBUSY or something. This ensures there are no events active for those vCPU tasks at VMENTER time and you can haz pass-through.
