Re: [Qemu-devel] kvm PCI assignment & VFIO ramblings

[Joerg Roedel <joerg.roedel@amd.com>]

On Mon, Aug 22, 2011 at 02:30:26AM -0400, 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)

That does not work. The bridge in question may not even be visible as a
PCI device, so you can't link to it. This is the case on a few PCIe
cards which only have a PCIx chip and a PCIe-2-PCIx bridge to implement
the PCIe interface (yes, I have seen those cards).

Regards,

	Joerg

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