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Re: UEFI support in ARM DomUs





On 18/06/2020 06:22, Oleksandr Andrushchenko wrote:

On 6/4/20 6:31 PM, Stefano Stabellini wrote:
On Thu, 4 Jun 2020, Oleksandr Andrushchenko wrote:
On 6/4/20 4:57 AM, Peng Fan wrote:
Grall <julien@xxxxxxx>;
Nataliya Korovkina <malus.brandywine@xxxxxxxxx>
Subject: UEFI support in ARM DomUs
We have made U-Boot run inside XEN DomU, but just only PV console part,
not implement other frontend drivers currently. Would this help for your
case if enable EFI in U-Boot?
Well, we have a working PV block implementation on top of that on iMX8

platform, mostly ported from mini-os. Currently we are finalizing the work

and cleaning up (it's going to take a week or so hopefully). Then, we we'll post

it on our public github. We are also thinking about upstreaming the work, but 
it may

take quite some time if the whole idea fits u-boot's view on such an extension 
at all.
Yes please to both of you! :-)

In the meantime, while we wait for those changes to go upstream in
uboot, could you please post a branch on github and a link on this email
thread?

It took a bit more time than we expected, but here we go [1]:

this is in form of a pull-request as we would love to hear from the

community and it is easier to discuss the code (please leave comments there)

1. There is code originating from MiniOS and work done by Peng, so we

would like to ask the respective copyright owners to raise their hands and

Not everyone are closely watching xen-devel. So if you want to find out who are the copyright owners, then your best solution is to go through the git log and CC the authors.


let us *fix inappropriate licensing* if any.

2. Please note, the series has a HACK to move the RAM base as it is expected by

our test platform (iMX8), so others will need to remove or modify that.

3. There is a limitation already noted by Peng that we do not have serial output

until MMU is setup, so we have introduced xen_early_printk helper which always

works, so you can use that for early stage debugging.

4. Minimal memory size supported is ~129M because of dtb placement by Xen tools

Hmmm... Why? What's wrong with booting a guest with just 64MB?


5. We use -D__XEN__ to access some of the hidden defines we need such as

GUEST_RAM0_BASE and the friends as there is no other way but manually defining 
the

same which is not cute.

I have replied to this in the pull request. But I want to bring the conversation here to have a wider discussion.

For a first, __XEN__ should really only be defined by the hypervisor and not used by the guest. This is used to gate non-stable ABI (such as the tools) and anything behind it hasn't been vetted to work in other build configuration that the one used by Xen.

In general, we expect the guest to discover everything for the device-tree because the memory layout is not stable (we want to be able to reshuffle as we add more features).

I know that EDK2/Tianocore can be built once and work on every Xen configuration. It would be ideal that U-boot follow the same. If it is really not possible, then we should explore a path that is preventing to define __XEN__.

How much does U-boot expect to know about the memory layout? Does it require to know all the memory banks? Or would it be sufficient for it to know the start address of the first bank and the minimum of RAM?

Cheers,

--
Julien Grall



 


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