Re: [PATCH v2 08/15] x86/hyperlaunch: locate dom0 kernel with hyperlaunch

[Jan Beulich <jbeulich@suse.com>]

On 30.01.2025 22:14, Stefano Stabellini wrote:
> On Thu, 30 Jan 2025, Jan Beulich wrote:
>> On 26.12.2024 17:57, Daniel P. Smith wrote:
>>> Look for a subnode of type `multiboot,kernel` within a domain node. If found,
>>> process the reg property for the MB1 module index. If the bootargs property is
>>> present and there was not an MB1 string, then use the command line from the
>>> device tree definition.
>>
>> While multiboot is apparently the first x86-specific part (as far as Xen goes)
>> to be put under domain-builder/, I wonder:
>> - Wouldn't looking for "multiboot,kernel" simply yield nothing on non-x86,
>>   so having the code under common/ would still be okay?
> 
> One small clarification: multiboot,kernel is actually common between
> both ARM and x86. It is "module-index" which is x86-specific and would
> "simply yield nothing on non-x86", as you wrote.
> 
> I'll let Dan address your point that "having the code under common/
> would still be okay".
> 
> 
>> - What's "multiboot" describing here? The origin of the module? (What other
>>   origins would then be possible? How would MB1 and MB2 be distinguished?
>>   What about a native xen.efi boot?) A property of the kernel (when Linux
>>   doesn't use MB)?
> 
> Each device tree node has a compatible string to qualify what kind of
> information the node is describing. The compatible string for device
> tree nodes describing a kernel binary or a ramdisk previously loaded
> into memory by a bootloader have a "multiboot," prefix. See
> docs/misc/arm/device-tree/booting.txt. This is unrelated to the binary
> multiboot protocol Grub uses on x86 to boot Xen.
> 
> A distinction between MB1 and MB2 is not needed in device tree, that
> information is retrieved via the Grub multiboot protocol as usual. The
> only thing needed here in device tree is the location of the kernel,
> either by RAM address, or by Grub multiboot module index. This last
> option (Grub multiboot module index) is the "module-index" property I
> mentioned above.

Hmm, then I'm afraid I can't make sense of the mentioning of MB1 in the
description. Yet that's a point more towards Daniel than you.

Jan