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Re: [Xen-devel] resume of HVM guest without PV drivers

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] resume of HVM guest without PV drivers
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 07 Aug 2009 10:44:36 +0100
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Thread-topic: [Xen-devel] resume of HVM guest without PV drivers
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So you're interested in a scenario that is PV'ed-up enough to do hypercalls,
but not enough to talk xenbus?

If you only care about being able to poll for having migrated/saved, there
must be some other bit of state you can push to Xen that doesn't get
migrated/saved. Like, create an IPI event channel and poll its status

 -- Keir

On 07/08/2009 10:13, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

> Meanwhile I thought of a (theoretical) way, but to my surprise it wouldn't
> work: The guest vCPU-s could check their registered runstate areas' state
> field, which should be stale (i.e. not RUNSTATE_running), but the surprise
> (to me) was that this gets updated only on context switch in, not on
> switch out (which means that at present that field also cannot be used to
> determine whether a remote vCPU is currently running - another thing
> that I intended to exploit [accepting that the state maybe stale by the
> time it gets evaluated/used]).
> Fixing this is obviously trivial (under the premise that you'd take such a
> patch), but expected functionality then of course will depend upon this
> patch being present in hypervisors derived from older code bases.
> Jan
>>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 07.08.09 11:01 >>>
> No. Perhaps something could be added if it's useful.
>  -- Keir
> On 07/08/2009 09:34, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>> Does a HVM guest without PV drivers have any way to know it got resumed
>> after a migration or save/restore cycle?
>> Thanks, Jan
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