Re: [Xen-devel] [PATCH v7 2/3] * util/grub.d/20_linux_xen.in: Add xen_boot command support for aarch64

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/05/17 09:57, Fu Wei wrote:
> Hi Stefano,
>
> On 4 May 2017 at 04:53, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
>> On Wed, 3 May 2017, Andrew Cooper wrote:
>>> On 02/05/17 08:06, fu.wei@xxxxxxxxxx wrote:
>>>> From: Fu Wei <fu.wei@xxxxxxxxxx>
>>>>
>>>> This patch adds the support of xen_boot command for aarch64:
>>>>     xen_hypervisor
>>>>     xen_module
>>>> These two commands are only for aarch64, since it has its own protocol and
>>>> commands to boot xen hypervisor and Dom0, but not multiboot.
>>>>
>>>> For other architectures, they are still using multiboot and module
>>>> commands.
>>>>
>>>> Signed-off-by: Fu Wei <fu.wei@xxxxxxxxxx>
>>> Sorry if I am jumping in late and asking awkward questions, but what is
>>> special about Xen/aarch64 here?  Why is it using a non-standard entry
>>> mechanism?
>> Multiboot is not available on ARM. The boot protocol we have on ARM is
>> FDT based:
>>
>> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/misc/arm/device-tree/booting.txt
>>
>> We often refer to it as "multiboot for arm" but in fact it is not
>> related to the x86 multiboot in any way.
>>
>> In Grub, the two protocols (multiboot and
>> docs/misc/arm/device-tree/booting.txt) are kept clearly distinct
>> (55A687E5.4070106@xxxxxxxxx). Hence, the need for this patch.
> Exactly, great thanks for your explanation! :-)

So it really is an entirely custom Xen booting protocol.

It is unfortunate that this wasn't reviewed sensibly at the time (and
implemented in a project-neutral way), but it looks like the time to fix
that properly has long since passed.

~Andrew

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