Re: [Xen-devel] Xen ARM dom0less use PV drivers

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 10 Apr 2019, Julien Grall wrote:
> Hi,
> 
> CCing Stefano who is looking after dom0less.
>
> On 08/04/2019 03:17, jinchen wrote:
> > Hello experts:
> >  ?0?2 ?0?2 The xen 4.12 support the Dom0less VM that start domu from xen not
> > xl, but the PV drivers hasn't been supported.

That's right. Please refer to docs/misc/arm/device-tree/booting.txt for
examples on how to boot other VMs from Xen. Also, I wrote a more
detailed tutorial on how to use dom0less that I have yet to publish.
Stay tuned.


> > Do you have some guidance for how to enable PV drivers when using dom0less?

The first question would be, do you actually need PV drivers between the
dom0less VMs? Because PV drivers are still available for all VMs started
later from dom0. Also, if you just need a simple communication mechanism
between the dom0less VMs, it would be pretty simple to setup a shared
memory area between them. Otherwise, see below.


> >  ?0?2 ?0?2 Due to kernel use xenbus and xenstore to probe PV drivers, these
> > mechanism should?0?2remain for compatibility?
> >  ?0?2 ?0?2 Removal the xenstore mechanism to xen internal or some other way?
> >  ?0?2 ?0?2 Thank you very much??

If you really need PV drivers in dom0less VMs, then the first thing to
do would be to get xenstore up and running in a dom0less domU. It is a
matter of allocating the proper resources, such as the evtchn page. It
is also a matter of getting xenstore up and running even if it might have
to wait for xenstored in dom0 to be initialized before being able to
make a connection. I expect this not to be trivial. 

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