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

[David Vrabel <david.vrabel@citrix.com>]

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?

David

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