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

[Joanna Rutkowska <joanna@invisiblethingslab.com>]

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On 07/05/10 21:18, Jeremy Fitzhardinge wrote:
> On 07/01/2010 09:12 AM, Keir Fraser wrote:
>> On 01/07/2010 16:18, "Joanna Rutkowska" <joanna@invisiblethingslab.com>
>> wrote:
>>
>>   
>>> 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).
>>>     
>> Well it would be good to confirm first that this is a pv_ops domU issue. If
>> so, it can probably be solved with a command-line option or somesuch, even
>> if the default policy will not change.
>>   
> 
> So the problem is that dom0 does the S3 suspend/resume, and presumably
> its wallclock time is updated properly via Linux's normal mechanisms.

Yes.

> But the S3 suspend/resume is unnoticed by all the domUs, so they don't
> know that an enormous amount of time has passed in an instant?

Correct. I don't think DomU are notified in any way about system suspend
-- at least nothing is in the dmesg/messages logs.

BTW: wouldn't it be good to actually notify them? Consider e.g. DomU
that has some device assigned to it (say a NIC) -- if we emulated S3
suspend/resume for this DomU, there is a hope it would properly
suspend/reinitialize the NIC, wouldn't it?

> Does that affect all the guest clocks, or just wallclock?
> 
Not sure if I understand your question -- what do you mean by "all guest
clocks"? Like timers? They don't seem to be affected [*], as the apps
run smoothly.

joanna.

[*] Except for when running on Core i5 -- see my other question in a
different thread.


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