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

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@xxxxxxxxxx> wrote:
Hi Jan,

On 05/11/2014 17:15, Jan Beulich wrote:
Julien Grall <julien.grall@xxxxxxxxxx> 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
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

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.


Julien Grall

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