Re: [Xen-devel] RFC: making the PVH 64bit ABI as stableo

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 2 Jun 2015, Jan Beulich wrote:
> >>> On 02.06.15 at 17:11, <roger.pau@xxxxxxxxxx> wrote:
> > Hello,
> > 
> > The document describing the PVH interface was committed 9 months ago
> > [1], and since then there hasn't been any change regarding the
> > interface. PVH is still missing features in order to have feature parity
> > with pure PV, mainly:
> > 
> >  - DomU miration support.
> >  - PCI passthrough support.
> >  - 32bit support.
> >  - AMD support.
> > 
> > AFAICT however none of these features are going to change the current
> > ABI.
> 
> This your guess; I don't think there's any guarantee.

Let's make it a guarantee.


> The more that talk was about making PVH uniformly enter the kernel in
> 32-bit mode.

What talk? IRL talks are irrelevant in this context. If it is not on the
list, it doesn't exist.


> > PCI passthrough might expand it, by adding new hypercalls, but I
> > don't think this should prevent us from marking the current ABI as
> > stable. ARM for example doesn't have PCI passthrough yet or migration
> > support, but the ABI has been marked as stable.
> > 
> > To that end, I would like to request the 64bit PVH ABI to be marked as
> > stable for DomUs. This is needed so external projects (like PVH support
> > for grub2) can progress.
> 
> Understandable, but no, not before all the fixmes in the tree got
> dealt with.

What is your timeline for that? In fact does anybody have any timelines
for it?

We need to have a clear idea of what exactly needs to happen. We also
need to have confidence that is going to happen in a reasonable time
frame. At the moment we have some various mumblings about things, but we
don't have a clear breakdown of the outstanding work and names
associated with each work item.

Is anybody going to volunteer writing that todo list?

Are we going to be able to find enough volunteers with the right skills
to be confident that PVH is going to be out of "experimental" within a
reasonable time frame? It is clear that some of the clean-ups require an
hypervisor expert.

If not, I suggest we rethink our priorities and we consider dropping PVH
entirely. I don't think is fair to expect Roger or anybody else to keep
their efforts up on PVH, when actually we don't know if we'll be able to
land it.

Maybe we could focus on improving PV on HVM and its security. Maybe we
could resurrect Intel's HVM Dom0 project
(http://events.linuxfoundation.org/sites/events/files/slides/HVM%20Dom0.pdf).
Think of how much farther we would be if we didn't start PVH in the
first place.


P.S.
This message is not addressed to Jan in particular but to the larger Xen
community.

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