Re: kvm PCI assignment & VFIO ramblings

On Mon, 2011-08-22 at 09:30 +0300, Avi Kivity wrote:

On 08/20/2011 07:51 PM, Alex Williamson wrote:

quoted

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