Re: [PATCH 2/2] arm/efi: Use dom0less configuration when using EFI boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.09.2021 22:16, Stefano Stabellini wrote:
> On Thu, 16 Sep 2021, Jan Beulich wrote:
>> On 16.09.2021 17:07, Luca Fancellu wrote:
>>> I explain here my understanding on dom0less, this feature is used to start 
>>> domUs at
>>> Xen boot in parallel, the name is misleading but it doesn’t require dom0 to 
>>> be absent.
>>>
>>> So if you have a dom0 kernel embed in the image, it's completely fine to 
>>> start it and it 
>>> doesn’t have to be skipped.
>>>
>>> Here the possible user cases:
>>> 1) start only dom0 [dom0 modules on xen.cfg or embedded in Xen image]
>>> 2) start only domUs, true dom0less [no dom0 modules on xen.cfg or embedded 
>>> in Xen image, domUs on DT]
>>> 3) start dom0 and domUs [(dom0 modules on xen.cfg or embedded in Xen image) 
>>> and domUs on DT]
>>
>> If that's the intention - fine. Stefano?
> 
> What do you mean by dom0 modules embedded in the Xen image? I am not
> familiar with it, but I imagine it doesn't involve any multiboot,module
> nodes in device tree, right?

There's no DT interaction there afaict. See commit 8a71d50ed40b
("efi: Enable booting unified hypervisor/kernel/initrd images").

> Putting aside "dom0 modules embedded in Xen image" that I didn't fully
> understand, there are three ways to load Dom0:
> 
> - dom0 kernel (and ramdisk, optional) on xen.cfg
> - dom0 kernel (and ramdisk, optional) on device tree using the "reg" property
> - dom0 kernel (and ramdisk, optional) on device tree using the "uefi,binary" 
> property
> 
> Then, the other use cases are:
> 
> - true dom0less, domUs on device tree using the "reg" property
> - true dom0less, domUs on device tree using the "uefi,binary" property
> 
> And of course all the possible combinations between Dom0 and DomU
> loading.

Okay, so as Luca says "dom0less" is a misnomer really. I wasn't
aware of this.

Jan