Re: About runtime service for Xen on ARM

[Julien Grall <julien.grall@citrix.com>]

On 19/08/2015 23:27, Shannon Zhao wrote:
> Hi Julien,

Hi Shannon,

Sorry for the late answer I was on holiday. In general it's better to CC 
multiple person and the mailing list as we may not be able to answer in 
short time or not know the answer.

I've CCed the ML and few people which know better than me the status of 
EFI runtime.

> Do you know the status of runtime service for Xen on ARM? Does it
> support runtime service booting with DT? If not, is there a plan to
> support it?

There is no support of runtime EFI on ARM for now and I'm not aware of 
any short plan for this.

> In addition, if you know this, does it support runtime service for Xen
> on x86?

There is some on-going work for EFI runtime on x86. I'm not sure if it 
has been upstream (CCed Daniel for this).

Although, one of there is a fundamental difference between the UEFI boot 
on x86 and ARM. While the code is the same, on ARM the UEFI act as a 
stub and should not be able to communicate via exported variable with 
Xen (we clobber BSS just after the UEFI stub jump on the normal boot start).

I know that the ARM EFI stub is using some shared variable with Xen (I 
have in mind the memory banks see bootinfo). We are very lucky that it's 
working because the variable is living in initdata which somehow is part 
of text (I'm not sure why) and not BSS.
So we should either decide that the stub and xen should be able to 
communicate together or not.

I would be in favor of the former but I don't know what are the view of 
the others.

Regards,

-- 
Julien Grall