Re: Xen nested wiki

[George Dunlap <george.dunlap@eu.citrix.com>]

On 02/14/2014 01:13 AM, Zhang, Yang Z wrote:
> Dario Faggioli wrote on 2014-02-13:
>> [Adding the Xen publicity mailing list]
>>
>> On gio, 2014-02-13 at 03:55 +0000, Zhang, Yang Z wrote:
>>> Hi George,
>>>
>>> I have updated the Latest Xen nested status in the Xen wiki page,
>>> please have a look.
>>>
>> Hey Yang,
>>
>> This is something really useful to have on the wiki, thanks for doing it.
>>
>>> Although it is hard to say nested is good supported or product
>>> quality, it is ready to let people to know nested basically is supported by Xen.
>>>
>> Right. With that in mind, I think this topic would be a great one for
>> a blog post on the Xen Project's blog! The content you have on the
>> wiki is mostly fine as the core content of the blog post too, we'd just need a couple more "colloquial"
>> glue paragraph here and there, both about nested virt in general and
>> about Xen supporting it, for instance...
>>
>>> Especially, for Xen on Xen case, I didn't see any issue with it for
>>> more than half
>> of year. Besides, I am always using nested Xen to debug Xen booting
>> issue which doesn't need to reboot my real box. And it really helps me a lot.
>> ...something like this line above... It's actually a quite good
>> example of what I meant above! :-)
>>
>> So, how do you feel about this?
>>
> Sure. If you can do it, that's great.
>
>>> So, if possible, I hope we can add nested support into Xen 4.4
>>> release to let people know current status.
>>>
>> Sorry for my ignorance on the subject, what is it that is missing for
>> making the above (and the content of the wiki) true for 4.4?
>>
> Sorry. I didn't clarify it clearly. Most of the patches to run nested are already in Xen upstream. What I want is to add "nested is basically supported in Xen 4.4" in the Xen 4.4 release note to let people know it.

I'm afraid "basically supported" will imply to people that they might 
consider shipping it on production systems.  But because of the issues 
with shadow-on-HAP, and the potential locking issues with the nested p2m 
table, both of which are in control of the guest admin rather than the 
host admin, I don't think that's a recommendation we can make at this time.

But I do think making some kind of announcement about common 
functionality being complete and ready to be tested would be a good 
idea.  When we come to make the release we can brainstorm on what 
wording to use.

Actually, I wonder whether advertising Win7's XP compatibility mode as a 
separate "tech preview" feature would make sense.  The people who use 
that feature are very likely very different than most other people who 
might think about using nested virtualization.

Also, re what's missing: We had a discussion a few weeks ago about what 
it might take to move nested virt out of "tech preview/experimental" 
mode.  I'll write those up and put them in my 4.4 planning e-mail so we 
can track the progress.

  -George