From mboxrd@z Thu Jan  1 00:00:00 1970
From: Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v3 kvmtool 00/11] Add PCI passthrough support with VFIO
Date: Wed, 15 Nov 2017 18:01:07 +0000
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Cc: Alex Williamson <alex.williamson@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Robin Murphy <Robin.Murphy@arm.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Marc Zyngier <Marc.Zyngier@arm.com>,
        Punit Agrawal <Punit.Agrawal@arm.com>
To: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
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On Wed, Nov 01, 2017 at 05:16:27PM +0000, Jean-Philippe Brucker wrote:
> On 31/10/17 21:17, Alex Williamson wrote:
> > On Tue, 31 Oct 2017 19:14:38 +0000
> > Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:
> > 
> >> This series implements PCI pass-through using VFIO in kvmtool. We
> >> introduce a new parameter to lkvm run, --vfio-group, that takes an IOMMU
> >> group number as argument, and passes all devices in the group to the
> >> guest.
> > 
> > Is there a discussion somewhere that provides the reasoning behind this
> > whole group choice?  It seems very limiting since there exist plenty of
> > examples of groups where endpoints and interconnects are both included,
> > but only the former is compatible with vfio-pci in the host.  It's
> > currently impossible to open all of these devices.  There's also no
> > opportunity to create different device topologies with this
> > specification (ex. multi-function vs separate devices vs downstream of
> > switches/bridges/root-ports).  It seems like a strange starting point
> > to me, but you probably already guessed that based on the QEMU
> > implementation.
> 
> I don't think it had come up yet. My guess is that it was simpler to do
> whole groups when writing the prototype (by Will) and I didn't think much
> about changing the interface when I took over. I agree that the QEMU
> parameter format is a lot better.
> 
> So maybe we should have "--vfio-pci [<domain>:]<bus>:<dev>.<fn>", and
> later "--vfio-platform <name.address>" etc.

That certainly looks much more expressive to me.

Will