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1What: /sys/kernel/iommu_groups/2Date: May 20123KernelVersion: v3.54Contact: Alex Williamson <alex.williamson@redhat.com>5Description: /sys/kernel/iommu_groups/ contains a number of sub-6 directories, each representing an IOMMU group. The7 name of the sub-directory matches the iommu_group_id()8 for the group, which is an integer value. Within each9 subdirectory is another directory named "devices" with10 links to the sysfs devices contained in this group.11 The group directory also optionally contains a "name"12 file if the IOMMU driver has chosen to register a more13 common name for the group.14Users:15 16What: /sys/kernel/iommu_groups/reserved_regions17Date: January 201718KernelVersion: v4.1119Contact: Eric Auger <eric.auger@redhat.com>20Description: /sys/kernel/iommu_groups/reserved_regions list IOVA21 regions that are reserved. Not necessarily all22 reserved regions are listed. This is typically used to23 output direct-mapped, MSI, non mappable regions. Each24 region is described on a single line: the 1st field is25 the base IOVA, the second is the end IOVA and the third26 field describes the type of the region.27 28 Since kernel 5.3, in case an RMRR is used only by graphics or29 USB devices it is now exposed as "direct-relaxable" instead30 of "direct". In device assignment use case, for instance,31 those RMRR are considered to be relaxable and safe.32 33What: /sys/kernel/iommu_groups/<grp_id>/type34Date: November 202035KernelVersion: v5.1136Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>37Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default38 domain in use by iommu for this group. See include/linux/iommu.h39 for possible read values. A privileged user could request kernel to40 change the group type by writing to this file. Valid write values:41 42 ======== ======================================================43 DMA All the DMA transactions from the device in this group44 are translated by the iommu.45 DMA-FQ As above, but using batched invalidation to lazily46 remove translations after use. This may offer reduced47 overhead at the cost of reduced memory protection.48 identity All the DMA transactions from the device in this group49 are not translated by the iommu. Maximum performance50 but zero protection.51 auto Change to the type the device was booted with.52 ======== ======================================================53 54 The default domain type of a group may be modified only when55 56 - The device in the group is not bound to any device driver.57 So, the users must unbind the appropriate driver before58 changing the default domain type.59 60 Unbinding a device driver will take away the driver's control61 over the device and if done on devices that host root file62 system could lead to catastrophic effects (the users might63 need to reboot the machine to get it to normal state). So, it's64 expected that the users understand what they're doing.65