Re: [PATCH v6 5/6] arm/dom0less: assign dom0less guests to cpupools

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.04.2022 10:54, Luca Fancellu wrote:
>> On 8 Apr 2022, at 13:10, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 08.04.2022 13:15, Luca Fancellu wrote:
>>>> On 8 Apr 2022, at 11:24, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>> On 08.04.2022 11:39, Luca Fancellu wrote:
>>>>>> On 8 Apr 2022, at 10:10, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>>>> On 08.04.2022 10:45, Luca Fancellu wrote:
>>>>>>> @@ -106,6 +106,8 @@ struct xen_domctl_createdomain {
>>>>>>> /* Per-vCPU buffer size in bytes. 0 to disable. */
>>>>>>> uint32_t vmtrace_size;
>>>>>>>
>>>>>>> + uint32_t cpupool_id;
>>>>>>
>>>>>> This could do with a comment explaining default behavior. In particular
>>>>>> I wonder what 0 means: Looking at cpupool_destroy() I can't see that it
>>>>>> would be impossible to delete pool 0 (but there may of course be
>>>>>> reasons elsewhere, e.g. preventing pool 0 to ever go empty) - Jürgen?
>>>>>> Yet if pool 0 can be removed, zero being passed in here should imo not
>>>>>> lead to failure of VM creation. Otoh I understand that this would
>>>>>> already happen ahead of your change, preventing of which would
>>>>>> apparently possible only via passing CPUPOOLID_NONE here.
>>>>>
>>>>> Pool-0 can’t be emptied because Dom0 is sitting there (the patch is 
>>>>> modifying
>>>>> cpupool_id only for DomUs).
>>>>
>>>> But we're talking about dom0less as per the subject of the patch here.
>>>
>>> Domains started using dom0less feature are not privileged and can’t do any 
>>> operation
>>> on cpu pools, that’s why I thought about Dom0.
>>
>> It's all a matter of XSM policy what a domain may or may not be able
>> to carry out.
> 
> Yes you are right, however I didn’t see so far this use case with a domU and 
> the tool stack,
> probably because it would need also xenstore etc… I’m aware that there is 
> some work going
> on to enable it also for dom0less domUs, so my question is:
> 
> Do you see this as a blocker for this patch? Are you ok if I send this patch 
> with just the comment
> below or in your opinion this patch requires some other work?

Agreement looks to be that there should be precautionary code added
to prevent the deleting of pool 0. This imo wants to be a prereq
change to the one here.

Jan