Re: [Xen-devel] [RFC PATCH KERNEL 0/4] x86/xen: untangle PV and PVHVM guest support code

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/14/2016 01:21 PM, David Vrabel wrote:
> On 14/11/16 17:17, Vitaly Kuznetsov wrote:
>> Hi,
>>
>> I have a long-standing idea to separate PV and PVHVM code in kernel and 
>> introduce Kconfig options to make it possible to enable the required
>> parts only breaking the current 'all or nothing' approach.
>>
>> Motivation:
>> - Xen related x86 code in kernel is rather big and it is unclear which
>>   parts of it are required for PV, for HVM or for both. With PVH coming
>>   into picture is becomes even more tangled. It makes it hard to
>>   understand/audit the code.
>>
>> - In some case we may want to avoid bloating kernel by supporting Xen
>>   guests we don't need. In particular, 90% of the code in arch/x86/xen/ is
>>   required to support PV guests and one may require PVHVM support only.
>>
>> - PV guests are supposed to go away one day and such code separation would
>>   help us to get ready.
> All good reasons.
>
>> This RFC adds XEN_PV Kconfig option and makes it possible to build PV-only
>> and PVHVM-only kernels. It also makes it possible to disable Dom0 support.
>> The series is incomplete and probably dirty in some places, I didn't pay
>> much attention to the current PVH implementation as (as far as I
>> understand) it is supposed to be replaced with PVHv2 but before investing
>> more I'd like to get opinions whether such refactoring will be welcomed.
> This series might be best done after PVHv1 is removed.  Boris, any
> thoughts on the best approach here?

I would prefer to wait until at least domU PVHv2 (together with removal
of v1) happens. As soon as I am done with ACPI hotplug on the hypervisor
side I will post the new version.

-boris

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