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Re: [Xen-devel] [PATCH]: xl: pci multi-function passthrough v2

To: Simon Horman <horms@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH]: xl: pci multi-function passthrough v2
From: Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>
Date: Tue, 10 Aug 2010 12:25:46 +0100
Cc: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On Mon, 2010-08-09 at 21:27 +0100, Simon Horman wrote:
> On Mon, Aug 09, 2010 at 01:00:39PM +0100, Gianni Tedesco wrote:
> > Changes since last time:
> >  1. Incorporate Stefanos feedback wrt. coding style, commenting
> >     non-obvious code and making single-function a special-case of
> >     multi-function
> >  2. Also fix the case for passing through a single sub-function and
> >     re-mapping it as a single-function virtual device. (ie: pfunc =
> >     non-zero, vfunc = zero). Apparently needed for SR-IOV.
> >  3. One-liner format change in xl pci-list-assignable to make it
> >    print a copy-and-pasteable BDF.
> > 8<----------------------------------------
> > 
> > Implement PCI pass-through for multi-function devices. The supported BDF
> > notation is: BB:DD.* - therefore passing-through a subset of functions or
> > remapping the function numbers is not supported except for when passing
> > through a single function which will be a virtual function 0.
> Is there any plan to extend this to allow for re-mapping and the like.
> When I worked on the original multi-function support (last year)
> this seemed to be a requirement of some people.

I am glad you asked

I initially planned to support this but it seemed like a nightmare:
1. The BDF notation practically becomes a regex language ;)
2. For HVM, if a function 0 is not passed through then you don't
   generate an SCI interrupt for PCI hotplug.
3. I couldn't imagine a scenario where this wasn't erroneous thing to do

But if someone can convince me that this is a worth-while thing to do
(3) then (1) and (2) are just technical problems which can be


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