Bug#599161: xen-linux-system-2.6.32-5-xen-amd64: Clock moved forward 50 minutes, caused Xen HVM domU restart
Hi Ben, Thanks for your response. See my responses inline.
On Wed, Oct 06, 2010 at 03:35:23AM +0100, Ben Hutchings wrote:
> On Tue, 2010-10-05 at 09:31 +0100, Mark Adams wrote:
> > Package: xen-linux-system-2.6.32-5-xen-amd64
> > Version: 2.6.32-21
> > Severity: important
> > Hi, Did you receive this bug report? I hadn't received a bug ID even
> > though receiving the copy of the original report.
> We don't have any other bug report with this description.
> > Likely because the address it was sent from originally was invalid.
> That would explain it.
> > -----------------
> > Hi All,
> > Im running Xen 4.0.1-rc6 Debian squeeze with pvops 2.6.32-21 kernel.
> > Today I noticed (when kerberos to the domain controllers stopped
> > working..) that the clock was 50 minutes out in dom0 -- This caused the
> > HVM windows domain controllers to have the wrong time.
> Since you appear to be in the UK, is it possible that the real-time
> clock is set to local time (GMT+1) while Xen expects it to be GMT, or
> vice versa?
The clock is set with tzdata as BST yes, it is also set to this in the
Windows server 2008 domU. We are using localtime=1 to match the clock
in dom0 to domU.
> (This doesn't explain why it's 50 minutes out rather than 1 hour. But
> ntpd will refuse to correct a large difference and the local clock may
> then drift further.)
> > Can anyone confirm whether xen controls the time or the kernel? Also
> > when I corrected the time in dom0 it was still wrong in HVM domU -- How
> > long does it take for this to propogate? (I rebooted the VM's to correct
> > it immediately).
> For HVM guests, the hypervisor emulates a standard PC real-time clock
> and the guest uses that to initialise the system time, but there is no
> way to force an update after the guest has booted unless the guest has
> specific support for Xen; I assume Citrix does provide such software for
> Windows but I don't know whether it is free software.
The citrix WHQL drivers might have this functionality, I don't use them
though - prefer the GPL PV drivers! (which don't have any clock support
as far as I can tell)
> For PV guests, I assume you can force an update to the guest time using
> the Xen management tools.
> Note, I'm just a general kernel maintainer and don't have any great
> knowledge of Xen.
All good, I have a feeling it might be a kernel issue rather than xen,
but I'm still not sure what actually -controls- the time, is it the
kernel? I think the key is in the log
Oct 2 18:50:33 havhost1 kernel: [623480.977748] Clocksource tsc unstable (delta = -2999660303788 ns)
As this is when the clock went from 18:00 to 18:50 and started the chain
of events (restarted the 2008 domU). Any ideas why this log occurred?
> Ben Hutchings
> Once a job is fouled up, anything done to improve it makes it worse.