Re: [tip:x86/mm] x86/mm/mtrr: Clean up mtrr_type_lookup()

Peter Zijlstra
2015-07-31T15:08:17Z

On Fri, Jul 31, 2015 at 04:44:52PM +0200, Borislav Petkov wrote:
> On Fri, Jul 31, 2015 at 03:18:02PM +0200, Peter Zijlstra wrote:
> > Using these functions with preemption enabled is racy against MTRR
> > updates. And if that race is ok, at the very least explain that it is
> > indeed racy and why this is not a problem.
>
> Right, so Luis has been working on burying direct MTRR access so
> after that work is done, we'll be using only PAT for changing memory
> attributes. Look at arch_phys_wc_add() and all those fbdev users of
> mtrr_add() which get converted to that thing...

Drivers don't do those lookups afaict.

But its things like set_memory_XX(), and afaict that's all buggy against
MTRR modifications.