Re: perf: rdpmc bug when viewing all procs on remote cpu

Vince Weaver
2019-01-11T21:52:27Z

On Thu, 10 Jan 2019, Vince Weaver wrote:

> On Thu, 10 Jan 2019, Vince Weaver wrote:
>
> > On Thu, 10 Jan 2019, Vince Weaver wrote:
> >
> > > However if you create an all-process attached to CPU event:
> > > perf_event_open(attr, -1, X, -1, 0);
> > > the mmap event index is set as if this were a valid event and so the rdpmc
> > > succeeds even though it shouldn't (we're trying to read an event value
> > > on a remote cpu with a local rdpmc).

so on further looking at the code, it doesn't appear that rdpmc events are
explicitly marked as unavailable in the attach-cpu or attach-pid case,
it's just by luck the check for PERF_EVENT_STATE_ACTIVE catches most of
the cases?

should an explicit check be added to zero out userpg->index in cases where
the event being measured is running on a different core?

Vince