0001 What: /sys/kernel/iommu_groups/
0002 Date: May 2012
0003 KernelVersion: v3.5
0004 Contact: Alex Williamson <alex.williamson@redhat.com>
0005 Description: /sys/kernel/iommu_groups/ contains a number of sub-
0006 directories, each representing an IOMMU group. The
0007 name of the sub-directory matches the iommu_group_id()
0008 for the group, which is an integer value. Within each
0009 subdirectory is another directory named "devices" with
0010 links to the sysfs devices contained in this group.
0011 The group directory also optionally contains a "name"
0012 file if the IOMMU driver has chosen to register a more
0013 common name for the group.
0014 Users:
0015
0016 What: /sys/kernel/iommu_groups/reserved_regions
0017 Date: January 2017
0018 KernelVersion: v4.11
0019 Contact: Eric Auger <eric.auger@redhat.com>
0020 Description: /sys/kernel/iommu_groups/reserved_regions list IOVA
0021 regions that are reserved. Not necessarily all
0022 reserved regions are listed. This is typically used to
0023 output direct-mapped, MSI, non mappable regions. Each
0024 region is described on a single line: the 1st field is
0025 the base IOVA, the second is the end IOVA and the third
0026 field describes the type of the region.
0027
0028 Since kernel 5.3, in case an RMRR is used only by graphics or
0029 USB devices it is now exposed as "direct-relaxable" instead
0030 of "direct". In device assignment use case, for instance,
0031 those RMRR are considered to be relaxable and safe.
0032
0033 What: /sys/kernel/iommu_groups/<grp_id>/type
0034 Date: November 2020
0035 KernelVersion: v5.11
0036 Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
0037 Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
0038 domain in use by iommu for this group. See include/linux/iommu.h
0039 for possible read values. A privileged user could request kernel to
0040 change the group type by writing to this file. Valid write values:
0041
0042 ======== ======================================================
0043 DMA All the DMA transactions from the device in this group
0044 are translated by the iommu.
0045 DMA-FQ As above, but using batched invalidation to lazily
0046 remove translations after use. This may offer reduced
0047 overhead at the cost of reduced memory protection.
0048 identity All the DMA transactions from the device in this group
0049 are not translated by the iommu. Maximum performance
0050 but zero protection.
0051 auto Change to the type the device was booted with.
0052 ======== ======================================================
0053
0054 The default domain type of a group may be modified only when
0055
0056 - The group has only one device.
0057 - The device in the group is not bound to any device driver.
0058 So, the users must unbind the appropriate driver before
0059 changing the default domain type.
0060
0061 Unbinding a device driver will take away the driver's control
0062 over the device and if done on devices that host root file
0063 system could lead to catastrophic effects (the users might
0064 need to reboot the machine to get it to normal state). So, it's
0065 expected that the users understand what they're doing.
