Re: [EXTERNAL] RE: [PATCH 0/5] Add new headers for Hyper-V Dom0

MUKESH RATHOR
2024-10-11T01:34:54Z

On 10/10/24 11:21, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent:
Thursday, October 3, 2024 12:51 PM
>>
>> To support Hyper-V Dom0 (aka Linux as root partition), many new
>> definitions are required.
>>
>> The plan going forward is to directly import headers from
>> Hyper-V. This is a more maintainable way to import definitions
>> rather than via the TLFS doc. This patch series introduces
>> new headers (hvhdk.h, hvgdk.h, etc, see patch #3) directly
>> derived from Hyper-V code.
>>
>> This patch series replaces hyperv-tlfs.h with hvhdk.h, but only
>> in Microsoft-maintained Hyper-V code where they are needed. This
>> leaves the existing hyperv-tlfs.h in use elsewhere - notably for
>> Hyper-V enlightenments on KVM guests.
>
> Could you elaborate on why the bifurcation is necessary? Is it an
> interim step until the KVM code can use the new scheme as well?
> Also, does "Hyper-V enlightenments on KVM guests" refer to
> nested KVM running at L1 on an L0 Hyper-V, and supporting L2 guests?
> Or is it the more general KVM support for mimicking Hyper-V for
> the purposes of running Windows guests? From these patches, it
> looks like your intention is for all KVM support for Hyper-V
> functionality to continue to use the existing hyperv-tlfs.h file.

Like it says above, we are creating new dom0 (root/host) support
that requires many new defs only available to dom0 and not any
guest. Hypervisor makes them publicly available via hv*dk files.

Ideally, someday everybody will use those, I hope we can move in
that direction, but I guess one step at a time. For now, KVM can
continue to use the tlfs file, and if there is no resistance, we
can move them to hv*dk files also as next step and obsolete the
single tlfs file.

Since headers are the ultimate source of truth, this will allow
better maintenance, better debug/support experience, and a more
stable stack. It also enforces non-leaking of data structs from
private header files (unfortunately has happened).

Thanks
-Mukesh