Does Xen support nested VM migration

Does Xen support nested VM migration

[Han, Huaitong]

Hi, all,
 
When I create a L1 guest with nestedhvm=1, and create a L2 guest in L1
guest, then migrate L1 guest, but the operation fails, and I find the
bugfix requires a lot of work.

Does Xen support the operation? I guess the nestedvm migration feature
is not at all implemented.

Thanks a lot
Huaitong

Re: Does Xen support nested VM migration

[Andrew Cooper]

On 01/07/2015 03:49, Han, Huaitong wrote:
> Hi, all,
>  
> When I create a L1 guest with nestedhvm=1, and create a L2 guest in L1
> guest, then migrate L1 guest, but the operation fails, and I find the
> bugfix requires a lot of work.

Fails in what way?

> Does Xen support the operation? I guess the nestedvm migration feature
> is not at all implemented.

Nested virtualisation is still experimental, and there are areas with
known issues, and scenarios which I expect have never been tried.

Having said that, there is nothing I am of with migration which I would
expect to break or need further fixing in a nested scenario.

~Andrew

Re: Does Xen support nested VM migration

[Han, Huaitong]

On Wed, 2015-07-01 at 08:50 +0100, Andrew Cooper wrote:
> On 01/07/2015 03:49, Han, Huaitong wrote:
> > Hi, all,
> >  
> > When I create a L1 guest with nestedhvm=1, and create a L2 guest in L1
> > guest, then migrate L1 guest, but the operation fails, and I find the
> > bugfix requires a lot of work.
> 
> Fails in what way?
The xen hypervisor in L1 guest has execute "vmxon" and
nvmx->vmxon_region_pa get the value, after L1 migration, vmxon impact is
lost and nvmx->vmxon_region_pa==0 , when L2 guest has some operation
like VMREAD or VMWRITE,  vmx_inst_check_privilege will return 1, and L1
guest maybe hang or panic.

> 
> > Does Xen support the operation? I guess the nestedvm migration feature
> > is not at all implemented.
> 
> Nested virtualisation is still experimental, and there are areas with
> known issues, and scenarios which I expect have never been tried.
> 
> Having said that, there is nothing I am of with migration which I would
> expect to break or need further fixing in a nested scenario.
> 
> ~Andrew
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: Does Xen support nested VM migration

[Andrew Cooper]

On 01/07/15 09:56, Han, Huaitong wrote:
> On Wed, 2015-07-01 at 08:50 +0100, Andrew Cooper wrote:
>> On 01/07/2015 03:49, Han, Huaitong wrote:
>>> Hi, all,
>>>  
>>> When I create a L1 guest with nestedhvm=1, and create a L2 guest in L1
>>> guest, then migrate L1 guest, but the operation fails, and I find the
>>> bugfix requires a lot of work.
>> Fails in what way?
> The xen hypervisor in L1 guest has execute "vmxon" and
> nvmx->vmxon_region_pa get the value, after L1 migration, vmxon impact is
> lost and nvmx->vmxon_region_pa==0 , when L2 guest has some operation
> like VMREAD or VMWRITE,  vmx_inst_check_privilege will return 1, and L1
> guest maybe hang or panic.

Ah yes - I remember this now.  I raised it as a concern about a year ago
when rewriting migration and finding no information along these lines in
the migration stream.

To support this, you will need to add a new per-vcpu record in the
hypervisor migration stream which sends the VMX architectural state from
the source to the destination.

~Andrew