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Re: [Xen-users] [Xen-devel] Future of 32-bit PV support

On Thu, Aug 16, 2018 at 12:55 AM, Juergen Gross <jgross@xxxxxxxx> wrote:
On 16/08/18 08:51, Jan Beulich wrote:
>>>> On 16.08.18 at 08:32, <christopher.w.clark@xxxxxxxxx> wrote:
>> On Wed, Aug 15, 2018 at 11:17 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
>>> In the Xen x86 community call we have been discussing whether anyone
>>> really is depending on 32-bit PV guests. We'd like to evaluate whether
>>> anyone would see problems with:
>>> - deprecating 32-bit PV guest support in Xen, meaning that we'd
>>>   eventually switch to support 32-bit PV guests only via PV-shim from
>>>   Xen 4.12 or 4.13
>>> - dropping 32-bit PV support from upstream Linux kernel, resulting in
>>>   current 32-bit PV guests no longer being able to upgrade to the newest
>>>   kernel version any longer
>>> And related to that:
>>> - is there any Linux distribution still shipping 32-bit PV-capable
>>>   systems?
>>> - what about BSD? Is 32-bit PV support important there?
>> Juergen - just to be very clear about the scope here:
>> * would this proposal affect the ability to use a 32-bit dom0?
> If the Dom0 is to be PV - yes, of course. For the time being there's
> no complete PVH Dom0 support, so if 32-bit is needed here, PV is
> for now indeed the only option.

ack. I asked because it's not necessarily obvious to all that dom0 is included in the term "guest", and it widens the consequences of this change.

And to be more precise: the first step would be to remove 32-bit PV
support from upstream Linux kernel. This would result in the loss of
the ability to use a _new_ Linux (e.g. >= 4.20 / 5.0) as a 32-bit dom0.
A 32-bit dom0 using a kernel <= 4.19 would still work until we remove
32-bit PV support from the hypervisor (which we wouldn't do before full
support of PVH dom0, I guess).

That makes sense.

Is there a special reason you want to use a 32-bit dom0?

In short, no.
OpenXT currently uses a 32-bit PV dom0, but work is already under way to migrate to 64-bit. I think your proposal is justified and good.


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