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- What: /sys/kernel/iommu_groups/
- Date: May 2012
- KernelVersion: v3.5
- Contact: Alex Williamson <[email protected]>
- 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 <[email protected]>
- 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 <[email protected]>
- 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.
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