RE: [RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export pt_get_curr_event()

[Wang, Wei W]

On Tuesday, September 27, 2022 2:09 AM, Liang, Kan wrote:
> From my understanding of the host-guest mode, the host PT event never
> traces the guest no matter whether the guest enables PT. So when VM-entry,
> there is only a guest PT event or no event. If so, I think the perf tool should
> warn the user if they try to create a host event with !exclude_guest, since the
> host event never traces a guest.

Probably not from the perf side. It's actually an issue of the KVM's pt_mode:
How can KVM prevent host from profiling the guest when in host-guest mode?
Just a warning from the perf side wouldn't be enough. I think that's a wrong
assumption from KVM side. I had a plan to fix this one. Exposing the host event
can tell KVM if the host is profiling the guest or not (i.e. host-guest is allowed).