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

[Anthony Liguori <anthony@xxxxxxxxxxxxx>]

On Mon, Jan 8, 2018 at 10:13 AM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Mon, Jan 08, 2018 at 05:45:32PM +0000, 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.
>>
>> Doing this would be a departure from our uusual non-security-bug
>> process of committing changes to xen.git#staging, and then backporting
>> only after the patches have been sitting in xen.git#master for some
>> time.  It's also a departure from our usual security-bug process of
>> developing and testing and committing patches for all supported
>> versions in parallel.
>>
>> But this is not a usual situation.  This time, we don't have the time
>> to wait.
>>
>> Opinions ?
>
> <sighs>
>
> +1
>
> But I am not exactly sure how one would actually boot this hybrid thing.
>
> As in I didn't see any libxl patches, or hvmloader or any of that
> that would 'slurp' this up and make the 'xl create' work out of the box
> so that PV guests are booted as HVM.
>
> Or does the admin have to do some of the 'migration' themselves?

For the HVM approach, yes, self migration is needed.  I think it would be pretty
easy to write a script that worked with most configuration files to do the
conversion.

Regards,

Anthony Liguori


>
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