linux-kernel - [PATCH v3 21/25] iommu: Expose DMA domain strictness via sysfs

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Message-Id: <fca07df20f45952ff5c19b744fc87be777259594.1628094601.git.robin.murphy@arm.com>
Date:   Wed,  4 Aug 2021 18:15:49 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     joro@...tes.org, will@...nel.org
Cc:     iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        suravee.suthikulpanit@....com, baolu.lu@...ux.intel.com,
        john.garry@...wei.com, dianders@...omium.org, rajatja@...gle.com,
        chenxiang66@...ilicon.com,
        Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Subject: [PATCH v3 21/25] iommu: Expose DMA domain strictness via sysfs

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.

CC: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
Reviewed-by: John Garry <john.garry@...wei.com>
Signed-off-by: Robin Murphy <robin.murphy@....com>

---

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