Re: [Xen-devel] [PATCH v2 11/22] xen/x86: allow disabling emulated devices for HVM guests

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> Also, from a guest POV, how is the hw emulated local apic going to be
> used? Are we going to route the interrupts from virtual devices
> (netfront, blkfront) to the lapic? Or we just want it for the timer and
> ditch the PV timer?

Use the event channels for the PV. For PCIe devices (passthrough)
use the APIC.

> 
> I can see that this is more interesting for a PVH/HVMlite Dom0, but
> still in that case I'm not sure how a guest is supposed to interact with
> it. Will the PHYSDEV hypercalls route interrupts to the emulated local
> apic instead of pirqs event channels? Will we trap PCI/MSI/MSI-X
> configuration and emulate it?

The thought I had was that with VT-D posted interrupts would
do the heavy lifting. And when the interrupts do get to us and
have to vmexit - well we would do the normal HVM path for those
that are interested.

And for those that want the event callback vector - we can still
do that. I hadn't thought much of details on this yet -perhaps
this should be discussed next Developer summit to hash some of
this out.

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