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

[Wang, Wei W]

On Thursday, September 22, 2022 9:35 PM, Peter Zijlstra
> On Thu, Sep 22, 2022 at 12:58:49PM +0000, Wang, Wei W wrote:
> 
> > Add a function to expose the current running PT event to users. One
> > usage is in KVM, it needs to get and disable the running host PT event
> > before VMEnter to the guest and resumes the event after VMexit to host.
> 
> You cannot just kill a host event like that. If there is a host event, the guest
> looses out.

OK. The intention was to pause the event (that only profiles host info) when switching to guest,
and resume when switching back to host.

I don't think it is proper to directly disable it via clear MSR_IA32_RTIT_CTL, e.g. there
may be dangling PT bit in the interrupt status register, this invokes the PT interrupt handler
to re-enable it (for more details about the issue please see patch 3 commit).
Would you have any suggestions to pause it? 

Thanks,
Wei