RE: static-mem preventing dom0 from booting

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 5 Nov 2021, Penny Zheng wrote:
> > -----Original Message-----
> > From: Penny Zheng
> > Sent: Friday, November 5, 2021 11:23 AM
> > To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Wei Chen <Wei.Chen@xxxxxxx>
> > Subject: RE: static-mem preventing dom0 from booting
> > 
> > Hi Stefano
> > 
> > > -----Original Message-----
> > > From: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > > Sent: Friday, November 5, 2021 9:36 AM
> > > To: Penny Zheng <Penny.Zheng@xxxxxxx>
> > > Cc: sstabellini@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > > Subject: static-mem preventing dom0 from booting
> > >
> > > Hi Penny,
> > >
> > > I am trying to test the static-mem feature in Xen 4.16 but I am having
> > > some issues. I can boot a dom0less domU with static-mem configured
> > > correctly, but when I do so, dom0 doesn't boot any longer.
> > >
> > 
> > Hmm, In our first intention, dom0less is a mandatory option for static
> > allocation.
> > domU on static allocation shall boot when dom0 doesn't boot there.
> > 
> > We think that, nevertheless, dom0 memory range is allocated by Xen
> > automatically, and it leads to the unpredictability. Static allocation 
> > through
> > device tree configuration prefers the total static environment to avoid
> > unpredictability.
> > 
> > > In the same configuration, if I remove the static-mem related lines
> > > from the domU node on device tree, both dom0 and domU boot successfully.
> > >
> > > I am sure the dom0 memory range, allocated by Xen automatically, and
> > > the domU memory range, hand-picked by me, do not clash as you can see
> > > from the boot logs (appended).
> > >
> > > Am I missing anything in the configuration? I am using a ZCU102 board,
> > > the memory node on the host device tree is:
> > >
> > 
> > Are you suggesting one scenario where dom0 with static-mem domU?
> > 
> > Hmmm, one quick thought, it may not be working with vpl011 emulation.
> > When dom0 exists, vpl011 will take dom0 as backend, which requests event
> > channel, xen store, etc, involved to communicate. but static-mem domU
> > without CONFIG_XEN shall not handle it.
> > 
> 
> Digging on this, and my misunderstanding. Domain created through device tree
> shall use xen as backend, not dom0. I guess that only the one created by xl 
> is using
> dom0 as backend.
> 
> Nevertheless, if this is your scenario, where dom0 and static-mem domU(NO 
> CONFIG_XEN) co-exists,
> I'll test for you.

The scenario is extremely simple; you can see the full device tree
configuration in the attachment to my previous email.

- dom0
- dom0less domU with static-mem

That's it! So basically it is just a normal dom0 + dom0less domU
configuration, which already works fine, where I added static-mem to the
domU and suddenly dom0 (not the domU!) stopped working.