linux-kernel - Re: [KVM timekeeping fixes 1/4] Fix kvmclock bug

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Message-ID: <20100920154120.GB3088@amt.cnet>
Date:	Mon, 20 Sep 2010 12:41:20 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	kvm@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [KVM timekeeping fixes 1/4] Fix kvmclock bug

On Sat, Sep 18, 2010 at 02:38:12PM -1000, Zachary Amsden wrote:
> If preempted after kvmclock values are updated, but before hardware
> virtualization is entered, the last tsc time as read by the guest is
> never set.  It underflows the next time kvmclock is updated if there
> has not yet been a successful entry / exit into hardware virt.
> 
> Fix this by simply setting last_tsc to the newly read tsc value so
> that any computed nsec advance of kvmclock is nulled.
> 
> Signed-off-by: Zachary Amsden <zamsden@...hat.com>

Applied, thanks.

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