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Re: [Qemu-devel] [PATCH 02/13] iommu: IOMMU Groups

From: Alex Williamson
Subject: Re: [Qemu-devel] [PATCH 02/13] iommu: IOMMU Groups
Date: Fri, 11 May 2012 17:58:31 -0600

On Fri, 2012-05-11 at 16:39 -0700, Greg KH wrote:
> On Fri, May 11, 2012 at 04:55:41PM -0600, Alex Williamson wrote:
> > IOMMU device groups are currently a rather vague associative notion
> > with assembly required by the user or user level driver provider to
> > do anything useful.  This patch intends to grow the IOMMU group concept
> > into something a bit more consumable.
> > 
> > To do this, we first create an object representing the group, struct
> > iommu_group.  This structure is allocated (iommu_group_alloc) and
> > filled (iommu_group_add_device) by the iommu driver.  The iommu driver
> > is free to add devices to the group using it's own set of policies.
> > This allows inclusion of devices based on physical hardware or topology
> > limitations of the platform, as well as soft requirements, such as
> > multi-function trust levels or peer-to-peer protection of the
> > interconnects.  Each device may only belong to a single iommu group,
> > which is linked from struct device.iommu_group.  IOMMU groups are
> > maintained using kobject reference counting, allowing for automatic
> > removal of empty, unreferenced groups.  It is the responsibility of
> > the iommu driver to remove devices from the group
> > (iommu_group_remove_device).
> > 
> > IOMMU groups also include a userspace representation in sysfs under
> > /sys/kernel/iommu_groups.  When allocated, each group is given a
> > dynamically assign ID (int).  The ID is managed by the core IOMMU group
> > code to support multiple heterogeneous iommu drivers, which could
> > potentially collide in group naming/numbering.  This also keeps group
> > IDs to small, easily managed values.  A directory is created under
> > /sys/kernel/iommu_groups for each group.  A further subdirectory named
> > "devices" contains links to each device within the group.  The iommu_group
> > file in the device's sysfs directory, which formerly contained a group
> > number when read, is now a link to the iommu group.  Example:
> > 
> > $ ls -l /sys/kernel/iommu_groups/26/devices/
> <snip>
> As you are creating new sysfs files and directories, you need to also
> add the proper Documentation/ABI/ files at the same time.

I'll update.  Thanks,


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