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