Re: [RFC PATCH] xen/design: Add design for EFI dom0less system start

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

On 07/09/2021 07:52, Luca Fancellu wrote:
> Add a design describing a proposal to improve the EFI
> configuration file, adding keywords to describe domU
> guests and allowing to start a dom0less system.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
>   docs/designs/efi-arm-dom0less.md | 105 +++++++++++++++++++++++++++++++
>   1 file changed, 105 insertions(+)
>   create mode 100644 docs/designs/efi-arm-dom0less.md
>
> diff --git a/docs/designs/efi-arm-dom0less.md b/docs/designs/efi-arm-dom0less.md
> new file mode 100644
> index 0000000000..8d8fa2243f
> --- /dev/null
> +++ b/docs/designs/efi-arm-dom0less.md
> @@ -0,0 +1,105 @@
> +# Xen EFI configuration file
> +
> +The current configuration file used by Xen when it is started as an EFI
> +application is considering only the dom0 guest and doesn't have any
> +property to describe and load in memory domU guests.
From my understanding, the problem is less about properties (we already 
have them in the Device-Tree) but more about where are the binaries 
located in memory as we don't know in advance.
So I would like to propose something that build on top of the 
Device-Tree work we did. Note this is early thoughts.
The problematic nodes in the DT are:

        module@0x4a000000 {
            compatible = "multiboot,kernel", "multiboot,module";
            reg = <0x0 0x4a000000 0xffffff>;
            bootargs = "console=ttyAMA0 init=/bin/sh";
        };

        module@0x4b000000 {
            compatible = "multiboot,ramdisk", "multiboot,module";
            reg = <0x0 0x4b000000 0xffffff>;
        };

In particular the property "reg" cannot be known in advance because the 
UEFI stub will be responsible to load the binaries in memory.
What we could do is providing a list of binaries to load and associate a 
key for each of them. Something like:
binary=<binary> <key>
binary=<binary2> <key2>
....

We can then replace the property "reg" with a new property "uefi,key" 
that will contain the name of the binary.
What do you think?

Cheers,

--
Julien Grall