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

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.


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.


Julien Grall

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