66 lines
3.0 KiB
Plaintext
66 lines
3.0 KiB
Plaintext
What: /sys/kernel/iommu_groups/
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Date: May 2012
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KernelVersion: v3.5
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Contact: Alex Williamson <alex.williamson@redhat.com>
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Description: /sys/kernel/iommu_groups/ contains a number of sub-
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directories, each representing an IOMMU group. The
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name of the sub-directory matches the iommu_group_id()
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for the group, which is an integer value. Within each
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subdirectory is another directory named "devices" with
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links to the sysfs devices contained in this group.
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The group directory also optionally contains a "name"
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file if the IOMMU driver has chosen to register a more
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common name for the group.
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Users:
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What: /sys/kernel/iommu_groups/reserved_regions
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Date: January 2017
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KernelVersion: v4.11
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Contact: Eric Auger <eric.auger@redhat.com>
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Description: /sys/kernel/iommu_groups/reserved_regions list IOVA
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regions that are reserved. Not necessarily all
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reserved regions are listed. This is typically used to
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output direct-mapped, MSI, non mappable regions. Each
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region is described on a single line: the 1st field is
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the base IOVA, the second is the end IOVA and the third
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field describes the type of the region.
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Since kernel 5.3, in case an RMRR is used only by graphics or
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USB devices it is now exposed as "direct-relaxable" instead
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of "direct". In device assignment use case, for instance,
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those RMRR are considered to be relaxable and safe.
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What: /sys/kernel/iommu_groups/<grp_id>/type
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Date: November 2020
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KernelVersion: v5.11
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Contact: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
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Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
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domain in use by iommu for this group. See include/linux/iommu.h
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for possible read values. A privileged user could request kernel to
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change the group type by writing to this file. Valid write values:
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======== ======================================================
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DMA All the DMA transactions from the device in this group
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are translated by the iommu.
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DMA-FQ As above, but using batched invalidation to lazily
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remove translations after use. This may offer reduced
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overhead at the cost of reduced memory protection.
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identity All the DMA transactions from the device in this group
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are not translated by the iommu. Maximum performance
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but zero protection.
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auto Change to the type the device was booted with.
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======== ======================================================
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The default domain type of a group may be modified only when
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- The group has only one device.
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- The device in the group is not bound to any device driver.
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So, the users must unbind the appropriate driver before
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changing the default domain type.
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Unbinding a device driver will take away the driver's control
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over the device and if done on devices that host root file
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system could lead to catastrophic effects (the users might
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need to reboot the machine to get it to normal state). So, it's
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expected that the users understand what they're doing.
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