Re: [Xen-devel] xen 4.10.0: stubdomain for HVM guest fails to start unless qdisk backend is used?

[George Dunlap <dunlapg@xxxxxxxxx>]

On Fri, Mar 9, 2018 at 3:24 PM, Chris Brannon <cmb@xxxxxxxxx> wrote:
> I recently made a build of xen 4.10.0 and installed it.
> I have a pre-existing HVM guest that uses the following configuration:
> 1 hard drive using the phy disk backend.  The guest also uses a device
> model stubdomain.  After upgrading, it refuses to start, due to a
> stubdomain timeout:
>
> Parsing config from somedomain
> libxl: error: libxl_dm.c:2203:stubdom_xswait_cb: Domain 32:Stubdom 33 for 32 
> startup: startup timed out
> libxl: error: libxl_create.c:1538:domcreate_devmodel_started: Domain 
> 32:device model did not start: -9
> libxl: error: libxl_domain.c:1000:libxl__destroy_domid: Domain 
> 32:Non-existant domain
> libxl: error: libxl_domain.c:959:domain_destroy_callback: Domain 32:Unable to 
> destroy guest
> libxl: error: libxl_domain.c:886:domain_destroy_cb: Domain 32:Destruction of 
> domain failed
>
> There is nothing in the logs.
>
> I noticed that a similar guest was booting with no issue.  The
> difference was that the booting guest also had a CD-ROM attached.  That
> CD-ROM used the qdisk backend, because it is backed by an ISO9660 image file.
> I changed the disk parameter in the first non-booting guest so that it
> used the qdisk backend rather than phy, and it booted with no trouble.
>
> Has anyone else had an issue like this after upgrading to 4.10?  I did
> some searching, and I didn't find anything.  I'm a bit surprised by
> that.  Since this is so easy for me to reproduce, and no one else has
> mentioned it, I wonder if my build could be subtly broken somehow.

Can you attach the following?

* the output of `xl dmesg`
* the output of `dmesg`
* the config file for the guest

I just tested stubdoms with staging-4.10 and everything works
correctly *as long as dom0 is assigned all memory*.  If I limit the
amount of dom0 memory to 1GiB, then stubdomains *doesn't* work with
qdisk; only works with the defautl ("phy") backend.

/me investigates a bit further...

 -George

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