Re: [Xen-devel] Commit moratorium to staging

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 11/03/2017 02:52 PM, George Dunlap wrote:
> On 11/03/2017 02:14 PM, Roger Pau Monné wrote:
>> On Thu, Nov 02, 2017 at 09:55:11AM +0000, Paul Durrant wrote:
>>> Hmm. I wonder whether the guest is actually healthy after the migrate. One 
>>> could imagine a situation where the storage device model (IDE in our case I 
>>> guess) gets stuck in some way but recovers after a timeout in the guest 
>>> storage stack. Thus, if you happen to try shut down while it is still stuck 
>>> Windows starts trying to shut down but can't. Try after the timeout though 
>>> and it can.
>>> In the past we did make attempts to support Windows without PV drivers in 
>>> XenServer but xenrt would never reliably pass VM lifecycle tests using 
>>> emulated devices. That was with qemu trad, but I wonder whether upstream 
>>> qemu is actually any better particularly if using older device models such 
>>> as IDE and RTL8139 (which are probably largely unmodified from trad).
>>
>> Since I've been looking into this for a couple of days, and found no
>> solution I'm going to write what I've found so far:
>>
>>  - The issue only affects Windows guests.
>>  - It only manifests itself when doing live migration, non-live
>>    migration or save/resume work fine.
>>  - It affects all x86 hardware, the amount of migrations in order to
>>    trigger it seems to depend on the hardware, but doing 20 migrations
>>    reliably triggers it on all the hardware I've tested.
> 
> Not good.
> 
> You said that Windows reported that the login process failed somehow?
> 
> Is it possible something bad is happening, like sending spurious page
> faults to the guest in logdirty mode?
> 
> I wonder if we could reproduce something like it on Linux -- set a build
> going and start localhost migrating; a spurious page fault is likely to
> cause the build to fail.

Well, with a looping xen-build going on in the guest, I've done 40 local
migrates with no problems yet.

But Roger -- is this on emulated devices only, no PV drivers?

That might be something worth looking at.

 -George

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