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iommu: Expose DMA domain strictness via sysfs

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The sysfs interface for default domain types exists primarily so users
can choose the performance/security tradeoff relevant to their own
workload. As such, the choice between the policies for DMA domains fits
perfectly as an additional point on that scale - downgrading a
particular device from a strict default to non-strict may be enough to
let it reach the desired level of performance, while still retaining
more peace of mind than with a wide-open identity domain. Now that we've
abstracted non-strict mode as a distinct type of DMA domain, allow it to
be chosen through the user interface as well.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/0e08da5ed4069fd3473cfbadda758ca983becdbf.1628682049.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Robin Murphy 2021-08-11 13:21:35 +01:00 committed by Joerg Roedel
parent c208916fe6
commit 26225bea1d
2 changed files with 7 additions and 1 deletions
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6
Documentation/ABI/testing/sysfs-kernel-iommu_groups
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@ -42,8 +42,12 @@ Description: /sys/kernel/iommu_groups/<grp_id>/type shows the type of default
======== ======================================================
DMA All the DMA transactions from the device in this group
are translated by the iommu.
DMA-FQ As above, but using batched invalidation to lazily
remove translations after use. This may offer reduced
overhead at the cost of reduced memory protection.
identity All the DMA transactions from the device in this group
are not translated by the iommu.
are not translated by the iommu. Maximum performance
but zero protection.
auto Change to the type the device was booted with.
======== ======================================================

2
drivers/iommu/iommu.c
View File

@ -3268,6 +3268,8 @@ static ssize_t iommu_group_store_type(struct iommu_group *group,
req_type = IOMMU_DOMAIN_IDENTITY;
else if (sysfs_streq(buf, "DMA"))
req_type = IOMMU_DOMAIN_DMA;
else if (sysfs_streq(buf, "DMA-FQ"))
req_type = IOMMU_DOMAIN_DMA_FQ;
else if (sysfs_streq(buf, "auto"))
req_type = 0;
else