Re: [Xen-devel] REGRESSION: Xen 4.13 RC5 fails to bootstrap Dom0 on ARM

[Roman Shaposhnik <roman@xxxxxxxxxx>]

Hi Julien! First of all -- thank you so much for detailed explanations
-- this is very much appreciated.

A few questions still (if you don't mind):

On Wed, Dec 18, 2019 at 2:17 PM Julien Grall <julien@xxxxxxx> wrote:
>
> Hi Roman,
>
> On 18/12/2019 17:03, Roman Shaposhnik wrote:
> > On Wed, Dec 18, 2019 at 3:50 AM Julien Grall <julien@xxxxxxx> wrote:
> > So -- nothing boots directly by UEFI -- everything goes through GRUB.
> >
> > However, my understanding is that GRUB will detect devicetree
> > information provided by UEFI (even though devicetree command is
> > supposed to completely replace that). Hence it is possible that Linux
> > relies on some residuals left in memory by GRUB that Xen doesn't pay
> > attention to (but this is a pretty wild speculation only).
>
> While it goes through GRUB, it is a bootloader and will just act as a
> proxy for EFI. So EFI application such as Xen/Linux can still be loaded
> and take advantage of runtime servies if present/implemented.

Aha! So then it depends on Xen actually using those EFI services. Which
leads to my first question:
   1. would it be possible to stay completely with just devicetrees information
       by passing efi=no-rs to Xen?

> In fact most of people on Arm are using GRUB rather than EFI directly as
> this is more friendly to use.
>
> Regarding the devicetree, Xen and Linux will completely ignore the
> memory nodes in Xen if using EFI. This because the EFI memory map will
> give you an overview of the platform with the EFI regions included.

Aha! So in that sense it is a bug in Xen after all, right? (that's what you're
referring to when you say you now understand what needs to get fixed).

Thanks,
Roman.

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