[PATCH v4 21/24] iommu: Expose DMA domain strictness via sysfs

From: Robin Murphy
Date: Wed Aug 11 2021 - 08:22:58 EST


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@xxxxxxxxxxxxxxx>
Reviewed-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>

---

v3: Summarise the implications in the documentation for completeness
---
Documentation/ABI/testing/sysfs-kernel-iommu_groups | 6 +++++-
drivers/iommu/iommu.c | 2 ++
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-kernel-iommu_groups b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
index eae2f1c1e11e..b15af6a5bc08 100644
--- a/Documentation/ABI/testing/sysfs-kernel-iommu_groups
+++ b/Documentation/ABI/testing/sysfs-kernel-iommu_groups
@@ -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.
======== ======================================================

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 55ca5bf3cafc..b141161d5bbc 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3267,6 +3267,8 @@ 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
--
2.25.1