[Intel-gfx] [RFC 04/10] drm/i915: Expose a PMU interface for perf queries

[Peter Zijlstra]

On Tue, Aug 29, 2017 at 07:16:31PM +0000, Rogozhkin, Dmitry V wrote:
> > Pretty strict, people tend to get fairly upset every time we leak stuff.
> > In fact Debian and Android carry a perf_event_paranoid patch that
> > default disables _everything_ :-(
> 
> Can you say more on that for Debian and Android? What exactly they do?
> What is the value of perf_event_paranoid there? They disable everything
> even for root and CAP_SYS_ADMIN? But still they don't remove this from
> kernel on compilation stage, right? So users can explicitly change
> perf_event_paranoid to the desired value?

They introduce (and default to) perf_event_paranoid = 3. Which
disallows everything for unpriv user, root can still do things IIRC, I'd
have to dig out the patch.

This way apps have no access to the syscall, but you can enable it using
ADB by lowering the setting. So developers still have access, but
regular apps do not.