[libvirt] [PATCH v4 3/8] libxl: error out on not supported CPU mode, instead of silently ignoring

[Jim Fehlig]

On 02/26/2018 01:48 PM, Marek Marczykowski-Górecki wrote:
> On Mon, Feb 26, 2018 at 01:20:49PM -0700, Jim Fehlig wrote:
>> On 02/15/2018 02:47 PM, Marek Marczykowski-Górecki wrote:
>>> On Tue, Feb 13, 2018 at 09:02:35AM -0700, Jim Fehlig wrote:
>>>> It looks like we never answered my question from V3, i.e. should we change
>>>> the default mode in the post-parse callback if NUMA or CPU features are
>>>> defined within <cpu>?
>>>
>>> Hmm, but this means changing the config behind user's back, no?
>>
>> Well, sort of. But it is really just making the implicit explicit.
>>
>>> You have disabled nested HVM, upgrade, now you have enabled.
>>> Global switch is some consolation here, but is it enough?
>>
>> I _think_ so. With a global default that disables nesting, are there any
>> scenarios you envision where a previously disabled nesting becomes enabled
>> after upgrade?
> 
> Probably also importing VM from older libvirt. Not sure about migration?

If importing from an older libvirt, the newer libvirt would have nesting 
disabled by default. I don't see a problem in that case. The same should be true 
when migrating from older to new libvirt. The only interesting case is migrating 
from libvirt containing this work to one without it. And then, only when the 
config contains <cpu mode='host-passthrough'> and svm|vmx are not disabled. 
Support for settings under <cpu> are quite new to the libxl driver, so in 
practice encountering that case is unlikely.

Regards,
Jim