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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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
> > > > 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

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