From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: [PATCH v2 11/22] xen/x86: allow disabling emulated
 devices for HVM guests
Date: Fri, 10 Jul 2015 14:54:11 -0400
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To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>, Jun Nakajima <jun.nakajima@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Eddie Dong <eddie.dong@intel.com>, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Jan Beulich <jbeulich@suse.com>, xen-devel@lists.xenproject.org, Boris Ostrovsky <boris.ostrovsky@oracle.com>
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> 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.