Re: [PATCH v3 0/4] Intel MPX support

[Ingo Molnar <mingo@kernel.org>]

* Ren Qiaowei <qiaowei.ren@intel.com> wrote:

> >> MPX kernel code, namely this patchset, has mainly the 2 
> >> responsibilities: provide handlers for bounds faults (#BR), and 
> >> manage bounds memory.
> >
> > AFAICS the kernel side implementation causes no runtime overhead 
> > for non-MPX workloads, and also causes no runtime overhead for 
> > non-MPX hardware, right?
>
> Yes.

Actually, I think that's not entirely true.

For example if within the same mm there's a lot of non-MPX threads and 
an MPX thread, then the MMU notifier will be called for MMU operations 
of every non-MPX thread as well!

So MPX state of a thread will slow down all the other non-MPX threads 
as well.

The statement is only true for non-MPX tasks that have their separate 
mm's that does not have a single MPX thread.

Thanks,

	Ingo