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

[Joanna Rutkowska <joanna@invisiblethingslab.com>]

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On 07/06/10 05:52, Keir Fraser wrote:
> On 05/07/2010 23:50, "Jeremy Fitzhardinge" <jeremy@goop.org> wrote:
> 
>>> 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?
>>>   
>>
>> I guess?  That implies some kind of PV S3 suspend and resume event to
>> feed into the dom U's device model.  What does 2.6.18-xen do?
> 
> I don't think our S3 support is very compatible with PV device passthrough.
> We support HVM virtual S3, and can S3-sleep HVM guests across real host S3,
> but we don't have similar for PV guests.
> 

How about implementing something very simple, like a notification via
xenstore (say, Dom0 would be setting some key)? Interested DomUs could
then register a watch, and get notified when the system was resumed from
S3. This would let them e.g. to call whatever hypercall is used normally
on DomU boot to sync DomU wallclock, or reinitialize/reconnect the NIC.

Obviously DomUs would not be notified when the system is just going to
sleep, as this would require some more sophisticated protocol (I guess
each DomU would have to ack within some given max timeout that it's done
with preparing from sleep?). But perhaps we can just ignore it? Even if
DomU has a NIC card assigned, wouldn't it be put to sleep by the
southbridge anyway? So, seems like we only care about the resume event?

joanna.


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