Re: Hand over of the Xen shared info page

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 19 May 2021, Julien Grall wrote:
> On 14/05/2021 10:50, Anastasiia Lukianenko wrote:
> > Hi Julien!
> 
> Hello,
> 
> > On Thu, 2021-05-13 at 09:37 +0100, Julien Grall wrote:
> > > 
> > > On 13/05/2021 09:03, Anastasiia Lukianenko wrote:
> > > The alternative is for U-boot to go through the DT and infer which
> > > regions are free (IOW any region not described).
> > 
> > Thank you for interest in the problem and advice on how to solve it.
> > Could you please clarify how we could find free regions using DT in U-
> > boot?
> 
> I don't know U-boot code, so I can't tell whether what I suggest would work.
> 
> In theory, the device-tree should described every region allocated in address
> space. So if you parse the device-tree and create a list (or any
> datastructure) with the regions, then any range not present in the list would
> be free region you could use.

Yes, any "empty" memory region which is neither memory nor MMIO should
work.


> However, I realized a few days ago that the magic pages are not described in
> the DT. We probably want to fix it by marking the page as "reserved" or create
> a specific bindings.
> 
> So you will need a specific quirk for them.

It should also be possible to keep the shared info page allocated and
simply pass the address to the kernel by adding the right node to device
tree. To do that, we would have to add a description of the magic pages
to device tree, which I think would be good to have in any case. In that
case it would be best to add a proper binding for it under the "xen,xen"
node.