Re: [Xen-devel] [PATCH RFC v1 00/13] Introduce HMV without dm and new boot ABI

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Jun 24, 2015 at 02:04:45PM +0200, Roger Pau Monné wrote:
> El 24/06/15 a les 13.52, Boris Ostrovsky ha escrit:
> > On 06/24/2015 06:14 AM, Roger Pau Monné wrote:
> >> El 24/06/15 a les 12.05, Jan Beulich ha escrit:
> >>>>>> On 24.06.15 at 11:47, <roger.pau@xxxxxxxxxx> wrote:
> >>>> What needs to be done (ordered by priority):
> >>>>
> >>>>   - Clean up the patches, this patch series was done in less than a
> >>>> week.
> >>>>   - Finish the boot ABI (this would also be needed for PVH anyway).
> >>>>   - Convert the rest of xc_dom_*loaders in order to use the physical
> >>>>     entry point when present, right now xc_dom_elfloader is the only
> >>>> one
> >>>>     usable with HVMlite. This is quite trivial (see patch 10, it's a 4
> >>>>     LOC change).
> >>>>   - Dom0 support.
> >>>>   - Migration.
> >>>>   - PCI pass-through.
> >>>>
> >>>> IMHO this is what we agreed to do with PVH, make it an HVM guest
> >>>> without
> >>>> a device model and without the emulated devices inside of Xen.
> >>>> Sooner or
> >>>> later we would need to make that change anyway in order to properly
> >>>> integrate PVH into Xen, and we get a bunch of new features for free as
> >>>> compared to PVH.
> >>>>
> >>>> I don't think of this as "throw PVH out of the window and start
> >>>> something completely new from scratch", we are going to reuse some of
> >>>> the code paths used by PVH inside of Xen. From a guest POV the changes
> >>>> needed to move from PVH into HVMlite are regarding the boot ABI only,
> >>>> which we already agreed that should be changed anyway.
> >>> I have to admit that I'm having a hard time making myself a clear
> >>> picture of what the intention now is, namely with feature freeze
> >>> being in about 2.5 weeks: If we assume that this series gets ready
> >>> in time, should we drop Boris' 32-bit support patches? Would then
> >>> be unfortunate if the series here didn't get ready.
> >> TBH I'm not going to make any promises of this being ready before the
> >> 4.6 feature freeze, not until I get some feedback from the tools
> >> maintainers regarding the libxc changes to unify the PV and HVM domain
> >> creation paths.
> > 
> > FWIW, I gave this a quick spin on Monday and crashed the hypervisor on a
> > NULL pointer right away in vapic code. Which, I assume, is not
> > surprising since we are not supposed to be there in the first place.
> > 
> > I'll try it again later today (I was out yesterday), maybe I messed
> > something up.
> 
> Yes, feature disabling is still not 100% done I'm afraid. For example if
> your hw supports vAPIC it will be enabled anyway, which can then lead to
> all kinds of trouble. As said, this is very initial and I've only tested
> it on one Nehalem box which doesn't have vAPIC.
> 
> >>
> >>> Otoh I don't think this and Boris' code conflict, and what we got in
> >>> the tree PVH-wise is kind of a mess right now anyway, so adding to
> >>> it just a few more bits (actually getting rid of some fixme-s, i.e.
> >>> reducing messiness), so I'd be inclined to take the rest of Boris'
> >>> series once ready, and if the series here gets ready too it could
> >>> then also go in. Which would then mean for someone (perhaps
> >>> after 4.6 was branched) to clean up any no longer necessary
> >>> PVH special cases, unifying things towards what we seem to now
> >>> call HVMlite.
> >> I'm not against merging the 32bit support series for PVH, but I'm
> >> certainly not going to invest time in adding 32bit PVH entry points to
> >> any OSes.
> > 
> > What about Tim's proposal
> > (http://lists.xen.org/archives/html/xen-devel/2014-12/msg00596.html)?
> > Can this work be made part of it? At least, make it extendable to that?
> 
> Yes, the aim of this work is to address some of the points expressed in
> that email, mainly merge PVH into HVM. But as we have already spoken,
> the entry point of HVMlite or whatever we call it is going to be
> different from the traditional PV/PVH entry point.

Right. If you were to take a sharpie where would you put in the 
list that Tim had written out?

And to my eye - it looks as the HVMLIte boot entry and the old PVH
bootpaths can co-exist for some time until they get merged together?

This would have the nice benefit of being able to troubleshoot
issues easier as you have an existing codepath for 'old-PVH' 
and new bootup path and can figure out what is missing to make it work
(with the Linux kernel at least).

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