1What: /sys/kernel/iommu_groups/ 2Date: May 2012 3KernelVersion: v3.5 4Contact: Alex Williamson <alex.williamson@redhat.com> 5Description: /sys/kernel/iommu_groups/ contains a number of sub- 6 directories, each representing an IOMMU group. The 7 name of the sub-directory matches the iommu_group_id() 8 for the group, which is an integer value. Within each 9 subdirectory is another directory named "devices" with 10 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 more 13 common name for the group. 14Users: 15 16What: /sys/kernel/iommu_groups/reserved_regions 17Date: January 2017 18KernelVersion: v4.11 19Contact: Eric Auger <eric.auger@redhat.com> 20Description: /sys/kernel/iommu_groups/reserved_regions list IOVA 21 regions that are reserved. Not necessarily all 22 reserved regions are listed. This is typically used to 23 output direct-mapped, MSI, non mappable regions. Each 24 region is described on a single line: the 1st field is 25 the base IOVA, the second is the end IOVA and the third 26 field describes the type of the region. 27 28 Since kernel 5.3, in case an RMRR is used only by graphics or 29 USB devices it is now exposed as "direct-relaxable" instead 30 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>/type 34Date: November 2020 35KernelVersion: v5.11 36Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> 37Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default 38 domain in use by iommu for this group. See include/linux/iommu.h 39 for possible read values. A privileged user could request kernel to 40 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 group 44 are translated by the iommu. 45 DMA-FQ As above, but using batched invalidation to lazily 46 remove translations after use. This may offer reduced 47 overhead at the cost of reduced memory protection. 48 identity All the DMA transactions from the device in this group 49 are not translated by the iommu. Maximum performance 50 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 when 55 56 - The group has only one device. 57 - The device in the group is not bound to any device driver. 58 So, the users must unbind the appropriate driver before 59 changing the default domain type. 60 61 Unbinding a device driver will take away the driver's control 62 over the device and if done on devices that host root file 63 system could lead to catastrophic effects (the users might 64 need to reboot the machine to get it to normal state). So, it's 65 expected that the users understand what they're doing. 66