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Re: [Xen-devel] write_tsc in a PV domain?

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] write_tsc in a PV domain?
From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 28 Aug 2009 16:30:46 +0100
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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> Jeremy's claim is that because some apps-that-use-
> rdtsc risk bugginess, Xen can claim rdtsc for its own
> use and effectively disallow all uses of rdtsc in any
> app by breaking the existing, sometimes-useful semantics
> of the instruction.

If Xen is hiding the tsc cpu feature from the kernel/apps it can. One
problem there is a lot of grotty code simply explodes without rdtsc

The alternative is to virtualise the TSC as some other hypedvisors do but
that has other impacts.

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