1 What: /sys/kernel/iommu_groups/ 1 What: /sys/kernel/iommu_groups/
2 Date: May 2012 2 Date: May 2012
3 KernelVersion: v3.5 3 KernelVersion: v3.5
4 Contact: Alex Williamson <alex.williamso 4 Contact: Alex Williamson <alex.williamson@redhat.com>
5 Description: /sys/kernel/iommu_groups/ cont 5 Description: /sys/kernel/iommu_groups/ contains a number of sub-
6 directories, each representing 6 directories, each representing an IOMMU group. The
7 name of the sub-directory matc 7 name of the sub-directory matches the iommu_group_id()
8 for the group, which is an int 8 for the group, which is an integer value. Within each
9 subdirectory is another direct 9 subdirectory is another directory named "devices" with
10 links to the sysfs devices con 10 links to the sysfs devices contained in this group.
11 The group directory also optio 11 The group directory also optionally contains a "name"
12 file if the IOMMU driver has c 12 file if the IOMMU driver has chosen to register a more
13 common name for the group. 13 common name for the group.
14 Users: 14 Users:
15 15
16 What: /sys/kernel/iommu_groups/reser 16 What: /sys/kernel/iommu_groups/reserved_regions
17 Date: January 2017 17 Date: January 2017
18 KernelVersion: v4.11 18 KernelVersion: v4.11
19 Contact: Eric Auger <eric.auger@redhat.c 19 Contact: Eric Auger <eric.auger@redhat.com>
20 Description: /sys/kernel/iommu_groups/reser 20 Description: /sys/kernel/iommu_groups/reserved_regions list IOVA
21 regions that are reserved. Not 21 regions that are reserved. Not necessarily all
22 reserved regions are listed. T 22 reserved regions are listed. This is typically used to
23 output direct-mapped, MSI, non 23 output direct-mapped, MSI, non mappable regions. Each
24 region is described on a singl 24 region is described on a single line: the 1st field is
25 the base IOVA, the second is t 25 the base IOVA, the second is the end IOVA and the third
26 field describes the type of th 26 field describes the type of the region.
27 27
28 Since kernel 5.3, in case an R 28 Since kernel 5.3, in case an RMRR is used only by graphics or
29 USB devices it is now exposed 29 USB devices it is now exposed as "direct-relaxable" instead
30 of "direct". In device assignm 30 of "direct". In device assignment use case, for instance,
31 those RMRR are considered to b 31 those RMRR are considered to be relaxable and safe.
32 32
33 What: /sys/kernel/iommu_groups/<grp_ 33 What: /sys/kernel/iommu_groups/<grp_id>/type
34 Date: November 2020 34 Date: November 2020
35 KernelVersion: v5.11 35 KernelVersion: v5.11
36 Contact: Sai Praneeth Prakhya <sai.prane 36 Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
37 Description: /sys/kernel/iommu_groups/<grp_ 37 Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
38 domain in use by iommu for thi 38 domain in use by iommu for this group. See include/linux/iommu.h
39 for possible read values. A pr 39 for possible read values. A privileged user could request kernel to
40 change the group type by writi 40 change the group type by writing to this file. Valid write values:
41 41
42 ======== ==================== 42 ======== ======================================================
43 DMA All the DMA transact 43 DMA All the DMA transactions from the device in this group
44 are translated by th 44 are translated by the iommu.
45 DMA-FQ As above, but using 45 DMA-FQ As above, but using batched invalidation to lazily
46 remove translations 46 remove translations after use. This may offer reduced
47 overhead at the cost 47 overhead at the cost of reduced memory protection.
48 identity All the DMA transact 48 identity All the DMA transactions from the device in this group
49 are not translated b 49 are not translated by the iommu. Maximum performance
50 but zero protection. 50 but zero protection.
51 auto Change to the type t 51 auto Change to the type the device was booted with.
52 ======== ==================== 52 ======== ======================================================
53 53
54 The default domain type of a g 54 The default domain type of a group may be modified only when
55 55
>> 56 - The group has only one device.
56 - The device in the group is n 57 - The device in the group is not bound to any device driver.
57 So, the users must unbind th 58 So, the users must unbind the appropriate driver before
58 changing the default domain 59 changing the default domain type.
59 60
60 Unbinding a device driver will 61 Unbinding a device driver will take away the driver's control
61 over the device and if done on 62 over the device and if done on devices that host root file
62 system could lead to catastrop 63 system could lead to catastrophic effects (the users might
63 need to reboot the machine to 64 need to reboot the machine to get it to normal state). So, it's
64 expected that the users unders 65 expected that the users understand what they're doing.
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