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+What: /sys/kernel/iommu_groups/
+Date: May 2012
+KernelVersion: v3.5
+Contact: Alex Williamson <alex.williamson@redhat.com>
+Description: /sys/kernel/iommu_groups/ contains a number of sub-
+ directories, each representing an IOMMU group. The
+ name of the sub-directory matches the iommu_group_id()
+ for the group, which is an integer value. Within each
+ subdirectory is another directory named "devices" with
+ links to the sysfs devices contained in this group.
+ The group directory also optionally contains a "name"
+ file if the IOMMU driver has chosen to register a more
+ common name for the group.
+Users:
+
+What: /sys/kernel/iommu_groups/reserved_regions
+Date: January 2017
+KernelVersion: v4.11
+Contact: Eric Auger <eric.auger@redhat.com>
+Description: /sys/kernel/iommu_groups/reserved_regions list IOVA
+ regions that are reserved. Not necessarily all
+ reserved regions are listed. This is typically used to
+ output direct-mapped, MSI, non mappable regions. Each
+ region is described on a single line: the 1st field is
+ the base IOVA, the second is the end IOVA and the third
+ field describes the type of the region.
+
+ Since kernel 5.3, in case an RMRR is used only by graphics or
+ USB devices it is now exposed as "direct-relaxable" instead
+ of "direct". In device assignment use case, for instance,
+ those RMRR are considered to be relaxable and safe.
+
+What: /sys/kernel/iommu_groups/<grp_id>/type
+Date: November 2020
+KernelVersion: v5.11
+Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
+Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
+ domain in use by iommu for this group. See include/linux/iommu.h
+ for possible read values. A privileged user could request kernel to
+ change the group type by writing to this file. Valid write values:
+
+ ======== ======================================================
+ DMA All the DMA transactions from the device in this group
+ are translated by the iommu.
+ DMA-FQ As above, but using batched invalidation to lazily
+ remove translations after use. This may offer reduced
+ overhead at the cost of reduced memory protection.
+ identity All the DMA transactions from the device in this group
+ are not translated by the iommu. Maximum performance
+ but zero protection.
+ auto Change to the type the device was booted with.
+ ======== ======================================================
+
+ The default domain type of a group may be modified only when
+
+ - The group has only one device.
+ - The device in the group is not bound to any device driver.
+ So, the users must unbind the appropriate driver before
+ changing the default domain type.
+
+ Unbinding a device driver will take away the driver's control
+ over the device and if done on devices that host root file
+ system could lead to catastrophic effects (the users might
+ need to reboot the machine to get it to normal state). So, it's
+ expected that the users understand what they're doing.