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Re: [Xen-devel] [rfc 00/18] ioemu: use devfn instead of slots as the uni

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [rfc 00/18] ioemu: use devfn instead of slots as the unit for passthrough
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Mon, 2 Mar 2009 22:25:57 +1100
Cc: Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
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On Mon, Mar 02, 2009 at 10:08:29AM +0000, Keir Fraser wrote:
> On 02/03/2009 09:53, "Simon Horman" <horms@xxxxxxxxxxxx> wrote:
> >> Not really what I had in mind. Xend can do the GSI->slot mapping, to ensure
> >> non-conflicting GSIs. I don't think any hypervisor changes are required, 
> >> let
> >> alone substantial ones.
> > 
> > Is the idea that xend would allocate a gsi to a device and
> > then pass that gsi along as part of the device configuration
> > to the device model?
> > 
> > If so, I think something similar to what I wrote, but moved
> > into xend could work quite well. But I sense that wasn't what
> > you had in mind either.
> I mean that xend can pick a virtual devfn for the device that it knows has a
> non-conflicting GSI. This avoids any need for dynamic mapping between devfn
> and GSI (which would be more of a pain in the neck -- for example, your
> patch doesn't work because certain parts of BIOS info tables need to be
> dynamically generated, as currently they hardcode the devfn-GSI
> relationship).

Thanks for the clarification. I suspect that scheme could easily run into
allocation problems when multi-function devices are passed-through as
multi-function devices.  Especially in the case of hot-plug. Buy which I
mean, it might be hard to find a device with the GSI for INTA + one or more
of INTB, C and D are free. But I'll take a look into it and see how it

In any case, could you be more specific about which areas my approach break?

Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H: www.vergenet.net/~horms/             W: www.valinux.co.jp/en

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