Re: [Xen-devel] [PATCH v3 13/24] xen/arm: Implement hypercall PHYSDEVOP_{, un}map_pirq

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-02-23 at 16:11 +0000, Julien Grall wrote:
> On 23/02/15 16:04, Ian Campbell wrote:
> > On Mon, 2015-02-23 at 15:53 +0000, Julien Grall wrote:
> >> Hi Ian,
> >>
> >> On 23/02/15 15:28, Ian Campbell wrote:
> >>> On Mon, 2015-02-23 at 09:33 +0000, Jan Beulich wrote:
> >>>>>>> On 20.02.15 at 17:53, <ian.campbell@xxxxxxxxxx> wrote:
> >>>>> Jan, do you have any feeling for how this is going to play out on x86
> >>>>> with the vapic stuff?
> >>>>
> >>>> The vapic logic shouldn't require any physdevop involvement, so if
> >>>> I read right what you propose (not having such a requirement /
> >>>> connection on ARM) either, I agree that a new domctl should be all
> >>>> that's needed (if XEN_DOMCTL_{,un}bind_pt_irq can't be re-used).
> >>>
> >>> Actually, I think bind_pt_irq with a new PT_IRQ_TYPE_* would be a good
> >>> option.
> >>>
> >>> An ARM SPI is a bit like an ISA IRQ, but not close enough to reuse IMHO
> >>> (and the datatype would need widening).
> >>
> >> We have to think about MSI and other type too...
> >>
> >> In any case a DOMCTL is not suitable here because a guest kernel may
> >> need to map/unmap IRQ too (think about ACPI or device passthrough).
> > 
> > I don't follow, setting up device passthrough is very much a toolstack
> > operation, isn't it? Where does the guest kernel get involved?
> 
> Sorry I meant the DOM0 kernel.
> 
> Not really. On platform device pass-through there is no way to know the
> IRQ, so for now the routing is done by the toolstack.
> 
> But we could decide to implement a driver in DOM0 which will
> unbind/bind/reset device.

Sure, but...

>  In this case it will require to
> assign/deassign the IRQ from DOM0.

...why does that follow?

> There is also the case of MSI.

Handled via XEN_DOMCTL_bind_pt_irq for the toolstack configuration
angle, the actual guest usage of them is a separate interface which
doesn't yet concern us, at least not in this series.

> > As for ACPI, I think dom0 propagating ACPI derived platform info to Xen
> > should be handled differently (at the hypercall interface at least)
> > separate from passthrough.
> 
> There is no difference between routing because of ACPI and/or because
> pass-through. So this should be done the same way.

I'm not convinced. Routing all the IRQs is only one aspect of dom0
propagating ACPI derived platform info to Xen.

I suppose we will see once I look at the ACPI series. In the meantime I
think XEN_DOMCTL_bind_pt_irq matches your requirements in for this
series (and is a domctl so we aren't tied to it once we have a better
understanding of the other stuff).

Ian.


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