Re: [Xen-devel] Status of Nested Virt in 4.4 (Was: Re: Xen 4.4 development update)

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2014-01-16:
>>>> On 16.01.14 at 10:45, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 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"?

As you know, it hard to cover all nested testings. So currently, will only 
cover the following L1 hypervisors: Xen, KVM, VMware workstation, VMware ESX, 
Win7 xp Mode, Hyper-v and L2 guest are: xp_x86, xp_x64, win7_x86, win7_x64, 
win8_x86, win8_x64, rhel6_x86, rhel6_x64.
For L1 Xen, KVM, VMware workstation, VMware ESX, Win7 xp Mode, I can boot up 
all L2 guests.
And for Hyperv, there are some known issues. But I can boot all L2 guests with 
my workaround patch.
Here are two topic that are discussing in mailing list which will block hyper-v
http://www.gossamer-threads.com/lists/xen/devel/310569?do=post_view_threaded
http://www.gossamer-threads.com/lists/xen/devel/299986
Also there are two another issues which I am working on cooking patches.

BTW, all my testing is based on L2 EPT. It seems there are some issues with L2 
shadow page table that need deep investigatation.

As Andrew said, nested still in experimental stage, because there are still 
lots of scenarios I am not covered in my testing. So it may not accurate to say 
it is good supported. But I hope people know that the nested is ready to use 
now. And encourage them to try it and report bug to us to push nested move 
forward.

>> 
>> What do the hypervisor side maintainers think?
> 
> Indeed I'm not sure we're there yet, not the least considering the
> recent discussion between SVM and VMX folks about how to deal with a
> certain problem, where a regression on the SVM side was expected if
> the code would have got committed as is.
> 
> But in the end I think the VMX and SVM maintainers should have the
> final say on nVMX and nSVM support state.
> 
> Jan
> 
>> 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.
> 
>


Best regards,
Yang



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