From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoffer Dall <christoffer.dall@linaro.org>
Subject: Re: [RFC PATCH] KVM: arm/arm64: Don't let userspace update CNTVOFF
 once guest is running
Date: Thu, 9 Jul 2015 14:24:06 +0200
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Cc: Marc Zyngier <marc.zyngier@arm.com>,
	Claudio Fontana <claudio.fontana@huawei.com>,
	Jan Kiszka <jan.kiszka@web.de>,
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To: Peter Maydell <peter.maydell@linaro.org>
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On Thu, Jul 09, 2015 at 01:07:24PM +0100, Peter Maydell wrote:
> On 9 July 2015 at 13:05, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > As I understand it, the problem is that if we ever run a VCPU after
> > reading the value, and write back the value afterwards, you potentially
> > make time go backwards and get inconsistent views of time from different
> > VCPUs because they may have read the time before/after updating the
> > CNTVOFF.
> 
> Right, but I think if QEMU does that it's a bug (and more to
> the point I don't entirely understand why we would do that
> yet, even given that we don't have a distinction between
> "registers to sync always" and "registers to sync only on
> reset"...)
> 
I think we have evidence that it does that, but we don't know why/how.

-Christoffer