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

[Grygorii Strashko <grygorii_strashko@xxxxxxxx>]

On 06.08.25 11:48, Julien Grall wrote:
> 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."
Got it.

> Although, "required" might still be too strict because it looks like we would 
> provide a configuration for dom0_mem if it is not set.
Correct - it will be defaulted to MB(512) if not configured + log notification 
"PLEASE SPECIFY dom0_mem PARAMETER - USING 512M FOR NOW\n"

Thank you.

--
Best regards,
-grygorii