Re: [PATCH v2] xen/dom0less: arm: fix hwdom 1:1 low memory allocation

[Julien Grall <julien@xxxxxxx>]

Hi Grygorii,

On 06/08/2025 09:19, Grygorii Strashko wrote:
> Hi Julien,
>
> On 06.08.25 00:07, Julien Grall wrote:
> > Hi Grygorii,
> >
> > On 05/08/2025 20:00, Grygorii Strashko wrote:
> > > From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
> > >
> > > Call stack for dom0less hwdom case (1:1) memory:
> > > create_domUs
> > > |-construct_domU
> > >    |-construct_hwdom()
> > >      |-allocate_memory_11()
> > >
> > > And allocate_memory_11() uses "dom0_mem" as:
> > > min_low_order =
> > >    get_order_from_bytes(min_t(paddr_t, dom0_mem, MB(128)));
> > >
> > > In case of dom0less boot the "dom0_mem" is not used and defaulted to 0,
> >  From docs/mics/xen-command-linux.pandoc:
> >
> > ---
> >
> > ### dom0_mem (ARM)
> >  > `= <size>`
> >
> > Set the amount of memory for the initial domain (dom0). It must be
> > greater than zero. This parameter is required.
> >
> > ---
> >
> > If dom0_mem is effectively optional, then shouldn't the doc be updated?
> No. I think doc is correct because when regular Dom0(hwdom)(initial domain)
> is created code goes through regular Dom0 path and "dom0_mem" is 
> accounted for.
I understand this is used when dom0 is not described in the device tree.
The crucial part in your sentence is "when", to me this indicates a 
condition. Whereas the current wording in xen-command-linux is using 
"required" with no condition. So a reader can rightfully think the 
parameter is also used in dom0less and have to be specified.
So I think the wording needs to be tweaked to something like "This 
parameter is required (and only used) when the initial domain is not 
described in the Device-Tree."
Although, "required" might still be too strict because it looks like we 
would provide a configuration for dom0_mem if it is not set.
Cheers,

--
Julien Grall