Re: [Xen-devel] Radical proposal: ship not-fully-tidied shim as 4.10.1

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Jan 09, 2018 at 01:24:02AM -0700, Jan Beulich wrote:
> >>> On 09.01.18 at 01:14, <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 08/01/2018 17:45, Ian Jackson wrote:
> >> AIUI we have a series for pv-in-pvh shim which is nearing completion
> >> in the sense that it will have been well-tested (especially the
> >> hypervisor parts) and has good functionality.  (Wei is handling the
> >> assembly of this series.)
> >>
> >> The series, however, needs proper review and tidying up.
> >> Specifically, it needs the kind of tidying up that fixes code
> >> structure and style issues that will hinder future Xen development.
> >> I.e. the kind of technical debt which does not directly cause bugs now
> >> but will cause trouble (including bugs) in the future.
> >>
> >> IMO that kind of tidying up is definitely essential for
> >> xen.git#master.  However, it is much less of an issue for Xen 4.10.
> >> Xen 4.10, as a stable branch, will get much more limited further
> >> development.  Failure to tidy things up there will make backporting
> >> other changes more awkward but the overall impact is both lower and
> >> time-bound.
> >>
> >> Currently the Xen Project has no published resolution for PV guests
> >> that can't be booted as, or converted to, PVH or HVM.  (And HVM guests
> >> bring their own problems.)  We need to provide our users with more
> >> good options as quickly as possible.
> >>
> >> I would like to suggest that a good way of doing this would be to ship
> >> the shim series as 4.10.1 within the next very few days.  It needs
> >> some minor bugfixing (build breakage etc.) but is basically ready for
> >> use.
> >>
> >> Speaking as a sysadmin (even, a very conservative sysadmin many of
> >> whose systems are running Debian oldstable), I have already taken a
> >> decision to rapidly advance to new software, in one context, because
> >> of these vulnerabilities - and take and fix whatever impact that has.
> >> I think many of our users would like to make the same choice.
> >>
> >> Releaseing 4.10.1 this week with pv-in-pvh support would give many of
> >> our users with PV guests an immediately deployable update, even though
> >> of course the version bump to get to 4.10 may be disruptive.
> 
> Such a version bump may be impossible to do for distros.
> Nevertheless I agree with the underlying idea, not the least
> because I expect distros with older hypervisors still wanting
> to use a 4.10 based shim (backporting host hypervisor and
> tool stack changes as necessary).
> 
> One thing I'd like to be considered though before rushing
> things into 4.10 (and, see below, staging as a prereq) is the
> goal of at least somewhat converging the two shim
> implementations. Especially from the tools side I understand
> that using the Citrix variant on anything older than 4.8 may
> end up being close to impossible, so at least for 4.7 and older
> the Amazon variant may be the only option. Hence as little
> divergence between the two as possible (within reasonable
> time constraints) would seem rather desirable.
> 

We haven't tested booting the series I posted in HVM mode, but off the
top of my head it should work in HVM mode as well -- the multiboot path
is left intact.

Wei.

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