Re: [Xen-devel] [RFC PATCH v1 10/10] xen/arm: GICv3 device tree parsing

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 24/03/14 17:34, Stefano Stabellini wrote:
> I think that for Dom0 we have to use vgic_v3, because it doesn't only
> give you support for more vcpus but also MSI and MSI-X delivery.
Right.

> For DomUs it might be important to support vgic_v2 on gicv3 hardware,
> however I wouldn't want to defer the decision to the user (i.e.
> introduce yet another VM config option), if not for debugging.
>
> Would it be possible to advirtise both gicv2 and gicv3 on device tree?
> What would the guest kernel do in that case?
Linux will try to load both GICv2 and GICv3 drivers. In any case I don't 
think it's a solution because:
        - you don't know how the kernel will react
        - how will you choose which backend to use?

> Otherwise we could default to vgic_v2 if vcpus <= 8 and vgic_v3 if
> vcpus > 8.
What about kernel which only support GICv3 and have less than 8 VCPUS?
What about of device (MSI, ...) passthrough with this kind of kernel?

I think we need to have a VM config option in this specific case.

Regards,

--
Julien Grall

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