linux-kernel - Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

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Message-ID: <1290191158.2109.1614.camel@laptop>
Date:	Fri, 19 Nov 2010 19:25:58 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Jason Wessel <jason.wessel@...driver.com>,
	Ingo Molnar <mingo@...e.hu>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

On Fri, 2010-11-19 at 11:59 -0500, Don Zickus wrote:
> Reading the kvm code in arch/x86/kernel/kvm/x86.c, it seems like they do
> _not_ fault on writes, only on some (which don't include a bunch of the
> perfctrs).  The reason seems to be to prevent older distros from falling
> apart that could not handle those faults properly.

Egads, that's just vile.. in that case we don't really need to do
anything, its a qemu/KVM bug, they emulate non-working hardware.

Hmm,. there is something we can do though, write a non-zero counter
value and then read it back, if its not what we wrote, its fudged and we
disable the pmu.


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