Re: [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware

Peter Zijlstra
2018-02-12T13:11:09Z

On Mon, Feb 12, 2018 at 12:27:19PM +0000, David Woodhouse wrote:
> On Mon, 2018-02-12 at 12:50 +0100, Peter Zijlstra wrote:

> > Wait, we're doing firmware from NMI? That sounds like a _REALLY_ bad
> > idea.
>
> And spin_lock_irqsave() too. Which is probably why I missed the fact
> that this was being called in NMI context.
>
> Yay for HP and their persistent attempts to "value subtract" in their
> firmware offerings.
>
> I'm tempted to drop that part of the patch and declare that if you're
> using this driver, the potential for stray branch prediction when you
> call into the firmware from the NMI handler is the *least* of your
> problems.

We should probably mark it BROKEN or something, or move it into staging.