linux-kernel - Re: [GIT PULL] EFI changes for v3.16

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Message-ID: <20140520202755.GI4798@console-pimps.org>
Date:	Tue, 20 May 2014 21:27:55 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	"Luck, Tony" <tony.luck@...el.com>
Subject: Re: [GIT PULL] EFI changes for v3.16

On Mon, 19 May, at 03:47:31PM, H. Peter Anvin wrote:
> 
> How on earth does this solve anything?  The only thing we add here is a
> WARN_ON_ONCE()... but the above text already tells us we have a problem.
> 
> It seems, rather, that we need to figure out how to deal with a pstore
> in this case.  There are a few possibilities:
> 
> 1. We could keep an XSAVE buffer area around for this particular use.
>    I am *assuming* we don't let more than one CPU into EFI, because I
>    cannot for my life imagine that this is safe in typical CPUs.
 
Correct. This is actually prohibited by the spec, so we have a lock to
enforce it.

> 2. Drop the pstore on the floor if !irq_fpu_usable().
> 
> 3. Allow the pstore, then die (on the assumption that we're dead
>    anyway.)

Personally, I'd prefer 2, but I'm open to suggestions.

-- 
Matt Fleming, Intel Open Source Technology Center
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