Re: [Xen-devel] [PATCH 5/7] xen: Make event channel work with PV featured HVM

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 8 Feb 2010, Sheng Yang wrote:
> We mapped each IOAPIC pin to a VIRQ, so that we can deliver interrupt through
> these VIRQs.
> 
> We used X86_PLATFORM_IPI_VECTOR as the noficiation vector for hypervisor
> to notify guest about the event.
> 
> The Xen PV timer is used to provide guest a reliable timer.
> 
> The patch also enabled SMP support, then we can support IPI through evtchn as 
> well.
> 
> Then we don't need IOAPIC/LAPIC...
> 

First of all I want to say that this series looks much better than the
previous one.

However I think there might still be some room for improvement:
wouldn't it make more sense to map vectors to event channels instead of
IOAPIC pins? This way it could work for MSI and passthrought devices
too. Also it would make sense to have a per-vector delivery option in
vlapic.c in xen: vlapic_set_irq should probably be the function that
decides how to inject the vector into the guest, either using the
classic emulated method or an event channel.
The decision should come from a matrix so that the guest might decide to
enable event channels on a per vector basis instead of having a single
global switch.
It seems to me that doing an intx to event channel translation in
hvm/irq.c is not the right thing in the right place.



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