Re: [PATCH v2 for 4.5] xen/arm: Add support for GICv3 for domU

[Julien Grall <julien.grall@linaro.org>]

Hi Konrad,

On 07/11/2014 15:45, Konrad Rzeszutek Wilk wrote:
> On Thu, Nov 06, 2014 at 10:27:41AM +0000, Julien Grall wrote:
>>
>>
>> On 06/11/2014 10:11, Jan Beulich wrote:
>>>>>> On 06.11.14 at 10:45, <julien.grall@linaro.org> wrote:
>>>> Hi Jan,
>>>>
>>>> On 05/11/2014 17:15, Jan Beulich wrote:
>>>>>>>> Julien Grall <julien.grall@linaro.org> 11/04/14 6:27 PM >>>
>>>>>> On 11/03/2014 04:39 PM, Konrad Rzeszutek Wilk wrote:
>>>>>>> It also needs Acks from Daniel and Jan.
>>>>>>
>>>>>> This patch doesn't modify the x86 part. So I'm not sure if Jan ack is
>>>>>> required. Would Ian C. ack be enough?
>>>>>
>>>>> Yes, it would.
>>>>>
>>>>>> Anyway, Jan do you have any objection on this patch?
>>>>>
>>>>> As said previously, I'm not particularly happy about it, but I also don't
>>>> strongly
>>>>> mind it going in in the current shape.
>>>>
>>>> May I ask what is wrong with the new approach to the a DOMCTL in this patch?
>>>>
>>>> The DOMCTL has been clearly identify as arm specific (there is "arm" in
>>>> the name). Therefore it doesn't seem necessary to expose it for other
>>>> architecture than ARM32 and ARM64.
>>>
>>> I didn't say there's anything actively wrong with it, all I said is that
>>> I'm not particularly happy about it: Irrespective of its name it doesn't
>>> look to be really arch-specific in the long run, plus it feels like the
>>> data being set here should rather be specified right at domain
>>> creation, or via a mechanism similar to x86'es HVM parameters (iirc
>>> the value set here can't be changed once the domain got first
>>> unpaused).
>>
>>
>> TBH I choose this solution because I though you would be disagree with
>> extending the domain create hypercall.
>>
>> In long run, there will be more parameters such as the number of spis. All
>> will be required at the same time. So the HVM parameters solution won't
>> really help here.
>>
>> However, I could give a look to extending the domain creation hypercall
>> (xen_domctl_createdomain) to add arch specific field.
>>
>> But I don't think it's Xen 4.5 material. So I would prefer to stay on this
>> approach for this release because we'd like to have GICv3 guest support on
>> Xen. Though I could rename the DOMCTL to DOMCTL_get_gic_version.
>
> That is a bit unfortunate as it sounds like that for Xen 4.6 you will
> then ditch this hypercall and focus on the new one? Won't this one then
> be bitrotten?

Unfortunately yes. Modifying the xen_domctl_createdomain hypercall at 
this time of the release is not safe. Even though I like challenge, I 
don't want do be blamed because of a bug that would slip the release date.

But, the DOMCTL interface is not considered as a stable ABI. I guess we
could kill this hypercall in Xen 4.6.

Regards,

-- 
Julien Grall