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

[Fu Wei <fu.wei@xxxxxxxxxx>]

Hi Andrew,

On 5 May 2017 at 17:01, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 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.

Yes, it is.

>
> 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.

I guess the reason Xen use an entirely custom(lightweight) booting
protocol on aarch64 is that the multiboot maybe a little "heavy" for
aarch64.

>
> ~Andrew



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat

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