From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Status of Nested Virt in 4.4 (Was: Re: Xen 4.4
 development update)
Date: Thu, 16 Jan 2014 10:03:35 +0000
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To: Ian Campbell <Ian.Campbell@citrix.com>
Cc: "Zhang, Yang Z" <yang.z.zhang@intel.com>, George Dunlap <george.dunlap@eu.citrix.com>, Tim Deegan <tim@xen.org>, Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xenproject.org>
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On 16/01/14 09:45, Ian Campbell wrote:
> On Thu, 2014-01-16 at 06:54 +0000, Zhang, Yang Z wrote:
>> Can I say nested virtualization also is good supported in Xen 4.4? 
> Can you enumerate the scenarios which have been tested and which you
> consider are "supported"?
>
> What do the hypervisor side maintainers think?

Absolutely still experimental.

>
> ISTR that not so long ago there were some quirks wrt not exposing the
> feature to guests and crashing if they used it, and another one a while
> back relating to a guest being able to enable nested virt on itself
> regardless of the host administrator's settings. I suppose they are both
> fixed but I wonder if the "command and control" side of nested virt has
> had the same level of consideration and testing as the actual
> functionality.
>
> Ian.

To the best of my knowledge, there are still deadlocks cases in the mm
code for interesting combinations of L1 and L2 memory styles such as
PoD/Paging.

See some of the concernes in the thread including Message-ID:
4A59A236-A272-471D-A061-A960E0CEFAAD@gridcentric.ca

~Andrew