Re: [PATCH 1/2] Fix perf LBR filtering

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Apr 25, 2013 at 07:00:37PM +0200, Andi Kleen wrote:
> > Traping the read deals with the first. The second shouldn't be a problem since
> > we generally only allow kernel info for CAP_ADMIN; if we don't already for LBR
> > that needs to be fixed separately.
> 
> Where is that check?  I don't see it.

Then that might need fixing.

> Also remember that precise == 2 can enable LBR implicitly.

Sure.. but it doesn't need the filter stuff. Now I completely forgot if it will
actually still use the filter muck.. /me goes check

I think intel_pmu_lbr_filter() will typically bail on the X86_BR_ALL test for
PEBS fixup, it might only end up in the filter code if precise_br_compat()
finds another LBR user compatible with the fixup.

> > That only leaves the third.. can we descern MMIO maps from the kernel page tables?
> 
> In theory you could use some bits in the PTE for vmalloc, but it would need quite a
> few changes.
> 
> Also there may be corner cases where MMIO is in the direct mapping or in
> the kernel mapping.

Hrmm... do we keep track of the MMIO regions somewhere at all?