Re: [PATCH v6 4/7] xen/arm: configure dom0less domain for enabling xenstore after boot

[Rahul Singh <Rahul.Singh@xxxxxxx>]

Hi Julien

> On 11 May 2022, at 10:18 am, Bertrand Marquis <Bertrand.Marquis@xxxxxxx> 
> wrote:
> 
> Hi Julien,
> 
>> On 11 May 2022, at 10:10, Julien Grall <julien@xxxxxxx> wrote:
>> 
>> Hi Bertrand,
>> 
>> On 11/05/2022 09:46, Bertrand Marquis wrote:
>>>> On 11 May 2022, at 09:38, Julien Grall <julien@xxxxxxx> wrote:
>>>> 
>>>> Hi Bertrand,
>>>> 
>>>> On 11/05/2022 08:46, Bertrand Marquis wrote:
>>>>>> On 10 May 2022, at 17:35, Julien Grall <julien@xxxxxxx> wrote:
>>>>>> 
>>>>>> Hi Rahul,
>>>>>> 
>>>>>> On 10/05/2022 17:30, Rahul Singh wrote:
>>>>>>>> + rc = evtchn_alloc_unbound(&alloc);
>>>>>>>> + if ( rc )
>>>>>>>> + {
>>>>>>>> + printk("Failed allocating event channel for domain\n");
>>>>>>>> + return rc;
>>>>>>>> + }
>>>>>>>> +
>>>>>>>> + d->arch.hvm.params[HVM_PARAM_STORE_EVTCHN] = alloc.port;
>>>>>>>> +
>>>>>>>> + return 0;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>> static int __init construct_domU(struct domain *d,
>>>>>>>> const struct dt_device_node *node)
>>>>>>>> {
>>>>>>>> @@ -3214,6 +3243,14 @@ static int __init construct_domU(struct domain 
>>>>>>>> *d,
>>>>>>>> if ( rc < 0 )
>>>>>>>> return rc;
>>>>>>>> 
>>>>>>>> + if ( kinfo.dom0less_enhanced )
>>>>>>> I think we need to do something like this to fix the error.
>>>>>>> if ( hardware_domain && kinfo.dom0less_enhanced )
>>>>>>> {
>>>>>>> }
>>>>>> 
>>>>>> Is there any use case to use "dom0less_enhanced" without dom0 (or a 
>>>>>> domain servicing Xenstored)?
>>>>>> 
>>>>> Just being curious here but would it even be possible to have non dom0 
>>>>> domain servicing xenstored ?
>>>> 
>>>> You can build Xenstored against mini-os and configure the init script to 
>>>> launch xenstored as a domain.
>>> So dom0 is not mandatory or should mini-os be started as Dom0 for this to 
>>> work ?
>> 
>> In order to allocate the event channel, you need to know the ID of the 
>> domain where Xenstored will run. Stefano's patch is relying on Xenstored to 
>> be run in Domain 0.
>> 
>> This would need to be updated if we want to run it in a separate domain.
> 
> Ok then Dom0 is mandatory at the moment, I am ok with that.
> 
>> 
>>>> 
>>>>>> If not, then I would consider to forbid this case and return an error.
>>>>> One way or an other we need to solve the crash but if it is forbidden we 
>>>>> must prevent coming to this step earlier as it means the configuration is 
>>>>> wrong.
>>>> 
>>>> I think this should be checked when parsing the configuration.
>>> If dom0 is mandatory yes, we should still make sure that this code cannot 
>>> be reached so an ASSERT would be nice here at least in case someone tries 
>>> to activate this code without dom0 (which might happen when we will push 
>>> the serie for static event channels).
>> 
>> I am fine with an ASSERT().
>> 
>> Are you saying that dom0less_enhanced will be set to true for the static 
>> event channel series?
>> 
>> If yes, then I think dom0less_enhanced will need to be an enum so we know 
>> what part of Xen is exposed.
> 
> No it won’t, we just need some of the changes done but without setting 
> dom0less_enhanced.
> @Rahul: can you confirm.
> 

We need to set the "xen,enhanced” enabled for dom0less domU to enable
the event-channel interface in dom0less guest. If we did not set this property 
we can’t
use the event-channel interface in dom0less domUs guests.

Regards,
Rahul
> Cheers
> Bertrand
> 
>> 
>> Cheers,
>> 
>> --
>> Julien Grall