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From: Andrew Lutomirski <amluto@gmail.com>
Date: Tue, 22 Apr 2014 18:23:23 -0700
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Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Alexander van Heukelum <heukelum@fastmail.fm>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>,
        Arjan van de Ven <arjan.van.de.ven@intel.com>,
        Brian Gerst <brgerst@gmail.com>,
        Alexandre Julliard <julliard@winehq.com>,
        Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>
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On Tue, Apr 22, 2014 at 6:17 PM, H. Peter Anvin <hpa@linux.intel.com> wrote:
> Another spin of the prototype.  This one avoids the espfix for anything
> but #GP, and avoids save/restore/saving registers... one can wonder,
> though, how much that actually matters in practice.
>
> It still does redundant SWAPGS on the slow path.  I'm not sure I
> personally care enough to optimize that, as it means some fairly
> significant restructuring of some of the code paths.  Some of that
> restructuring might actually be beneficial, but still...
>

What's the to_dmesg thing for?

It looks sane, although I haven't checked the detailed register manipulation.

Users of big systems may complain when every single CPU lines up for
that mutex.  Maybe no one cares.

--Andy