From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: kvm PCI assignment & VFIO ramblings
Date: Tue, 23 Aug 2011 06:53:46 +1000
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Cc: Alex Williamson <alex.williamson@redhat.com>,
	aafabbri <aafabbri@cisco.com>,
	Alexey Kardashevskiy <aik@au1.ibm.com>, kvm@vger.kernel.org,
	Paul Mackerras <pmac@au1.ibm.com>,
	qemu-devel <qemu-devel@nongnu.org>, chrisw <chrisw@sous-sol.org>,
	iommu <iommu@lists.linux-foundation.org>,
	Anthony Liguori <anthony@codemonkey.ws>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, benve@cisco.com
To: Avi Kivity <avi@redhat.com>
Return-path: <linux-pci-owner@vger.kernel.org>
In-Reply-To: <4E51F782.7060005@redhat.com>
Sender: linux-pci-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

On Mon, 2011-08-22 at 09:30 +0300, Avi Kivity wrote:
> On 08/20/2011 07:51 PM, Alex Williamson wrote:
> > We need to address both the description and enforcement of device
> > groups.  Groups are formed any time the iommu does not have resolution
> > between a set of devices.  On x86, this typically happens when a
> > PCI-to-PCI bridge exists between the set of devices and the iommu.  For
> > Power, partitionable endpoints define a group.  Grouping information
> > needs to be exposed for both userspace and kernel internal usage.  This
> > will be a sysfs attribute setup by the iommu drivers.  Perhaps:
> >
> > # cat /sys/devices/pci0000:00/0000:00:19.0/iommu_group
> > 42
> >
> 
> $ readlink /sys/devices/pci0000:00/0000:00:19.0/iommu_group
> ../../../path/to/device/which/represents/the/resource/constraint
> 
> (the pci-to-pci bridge on x86, or whatever node represents partitionable 
> endpoints on power)

The constraint might not necessarily be a device.

The PCI bridge is just an example. There are other possible constraints.
On POWER for example, it could be a limit in how far I can segment the
DMA address space, forcing me to arbitrarily put devices together, or it
could be a similar constraint related to how the MMIO space is broken
up.

So either that remains a path in which case we do have a separate set of
sysfs nodes representing the groups themselves which may or may not
itself contain a pointer to the "constraining" device, or we just make
that an arbitrary number (in my case the PE#)

Cheers,
Ben