Re: [Xen-devel] Radical proposal v2: Publish Amazon's verison now, Citrix's version soon

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.01.18 at 18:25, <sstabellini@xxxxxxxxxx> wrote:
> On Wed, 10 Jan 2018, George Dunlap wrote:
>> * Executive summary
>> 
>> - We've agreed on a "convergence" point for PV shim functionality that
>>   covers as many users as possible:
>>  - 'HVM' functionality: boots in HVM mode, has support for Xen 3.4
>>    event channels, &c, booted via 'sidecar'
>>  - 'PVH' functionality: boots in PVH mode, booted via toolstack
>>    changes
>> 
>> - "Vixen" (the Amazon shim) and PVH shim (mostly developed by Citrix)
>>   each cover some users and not others; neither one (yet) covers all
>>   users
> 
> Sorry for being punctilious, but neither one can cover all users: there
> are users without VT-x on their platform, and both approaches require
> VT-x.

For the record, yesterday I've decided to make an attempt to
create a very simplistic patch to deal with the issue in the
hypervisor, ignoring (almost) all performance considerations
(not all, because I didn't want to go the "disable caching" route).
I've dealt with some of the to-be-expected early bugs, but I'm
now debugging a host hang (note: not a triple fault apparently,
as the box doesn't reboot, yet triple faults is what I would have
expected to occur if anything is wrong here or missing).

I know that's late, and I have to admit that I don't understand
myself why I didn't consider doing such earlier on, but the
much increased pressure to get something like the shim out,
which
- doesn't address all cases
- requires changes to how VMs are being created (which likely will
  be a problem for various customers)
- later will want those changes undone
plus the pretty obvious impossibility to backport something like
Andrew's (not yet complete) series to baselines as old as 3.2
made it seem to me that some (measurable!) performance
overhead can't be all that bad in the given situation.

Jan


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