Re: S3 sleep in dom0 breaks dom0<->domU wallclock synchronization

[Joanna Rutkowska <joanna@invisiblethingslab.com>]

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On 07/01/10 16:50, Keir Fraser wrote:
> On 01/07/2010 04:04, "Rafal Wojtczuk" <rafal@invisiblethingslab.com> wrote:
> 
>> Hello,
>> xen-3.4.3 x86_64, dom0 2.6.34-9.xenlinux as dom0,
>> 2.6.32.14-1.2.105.pvops0 in PV domU. /proc/sys/xen/independent_wallclock is
>> 0.
>> After resume from S3 sleep in dom0, the wall clock in domU is
>> desynchronized from dom0's one (the delta is the length of S3 sleep). It
>> does not seem that adj_timex is in progress (the delta is constant in time).
>>
>> Is it a known issue ? If so, could someone point me to a solution ?
> 
> I think that pv_ops domU kernels pick up Xen's wallclock at boot time, but
> won't listen for updates thereafter. So if you ran a non-pv_ops domU, you'd
> probably find that its wallclock would be correctly updated after S3. Cc'ing
> Jeremy as he'll be able to confirm this. I think his answer will be that you
> should run ntp in every guest, but I'm not sure how that will react to
> unexpected warps in time.
> 
Actually we're running a pvops kernel in DomUs (in fact a fairly recent
pvops0, as we had some bad experience with regular Fedora kernels in DomU).

Running an NTP in every VM is not a good solution. Some VMs might be
forbidden any access to the network (e.g. my "vault" VM, that I use for
storing passwords, and other very sensitive stuff, doesn't have any
networking), while some other might be allowed only very limited network
traffic, e.g. only HTTPS to specific, white-listed servers (e.g.
"banking" VM).

joanna.


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