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Date: Mon, 12 Feb 2018 14:06:40 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
        Thomas Mingarelli <thomas.mingarelli@hpe.com>, hpa@zytor.com,
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        Dave Hansen <dave@sr71.net>, Borislav Petkov <bp@alien8.de>,
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Subject: Re: [tip:x86/pti] x86/speculation: Use IBRS if available before
 calling into firmware
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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.