Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
From: Peter Zijlstra <peterz@infradead.org>
To: Don Zickus <dzickus@redhat.com>
Cc: Jason Wessel <jason.wessel@windriver.com>, Ingo Molnar <mingo@elte.hu>,
        Robert Richter <robert.richter@amd.com>, ying.huang@intel.com,
        Andi Kleen <andi@firstfloor.org>, LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>
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Date: Fri, 19 Nov 2010 19:25:58 +0100
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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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