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From: Robin Murphy <robin.murphy@arm.com>
To: joro@8bytes.org, will@kernel.org
Cc: iommu@lists.linux-foundation.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, suravee.suthikulpanit@amd.com,
	baolu.lu@linux.intel.com, john.garry@huawei.com,
	dianders@chromium.org, rajatja@google.com,
	chenxiang66@hisilicon.com,
	Jean-Philippe Brucker <jean-philippe@linaro.org>
Subject: [PATCH v3 23/25] iommu: Merge strictness and domain type configs
Date: Wed,  4 Aug 2021 18:15:51 +0100	[thread overview]
Message-ID: <18f2757675b1a4d74d052b2b211e512ebf6e465e.1628094601.git.robin.murphy@arm.com> (raw)
In-Reply-To: <cover.1628094600.git.robin.murphy@arm.com>

To parallel the sysfs behaviour, merge the new build-time option
for DMA domain strictness into the default domain type choice.

Suggested-by: Joerg Roedel <joro@8bytes.org>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>

---

v3: Remember to update parameter documentation as well
---
 .../admin-guide/kernel-parameters.txt         |  8 +-
 drivers/iommu/Kconfig                         | 80 +++++++++----------
 drivers/iommu/iommu.c                         |  2 +-
 3 files changed, 44 insertions(+), 46 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 90b525cf0ec2..19192b39952a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2045,11 +2045,9 @@
 			1 - Strict mode.
 			  DMA unmap operations invalidate IOMMU hardware TLBs
 			  synchronously.
-			unset - Use value of CONFIG_IOMMU_DEFAULT_{LAZY,STRICT}.
-			Note: on x86, the default behaviour depends on the
-			equivalent driver-specific parameters, but a strict
-			mode explicitly specified by either method takes
-			precedence.
+			unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
+			Note: on x86, strict mode specified via one of the
+			legacy driver-specific options takes precedence.
 
 	iommu.passthrough=
 			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index c84da8205be7..6e06f876d75a 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -79,55 +79,55 @@ config IOMMU_DEBUGFS
 	  debug/iommu directory, and then populate a subdirectory with
 	  entries as required.
 
-config IOMMU_DEFAULT_PASSTHROUGH
-	bool "IOMMU passthrough by default"
-	depends on IOMMU_API
-	help
-	  Enable passthrough by default, removing the need to pass in
-	  iommu.passthrough=on or iommu=pt through command line. If this
-	  is enabled, you can still disable with iommu.passthrough=off
-	  or iommu=nopt depending on the architecture.
-
-	  If unsure, say N here.
-
 choice
-	prompt "IOMMU default DMA IOTLB invalidation mode"
-	depends on IOMMU_DMA
-
-	default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU)
-	default IOMMU_DEFAULT_STRICT
+	prompt "IOMMU default domain type"
+	depends on IOMMU_API
+	default IOMMU_DEFAULT_DMA_LAZY if AMD_IOMMU || INTEL_IOMMU
+	default IOMMU_DEFAULT_DMA_STRICT
 	help
-	  This option allows an IOMMU DMA IOTLB invalidation mode to be
-	  chosen at build time, to override the default mode of each ARCH,
-	  removing the need to pass in kernel parameters through command line.
-	  It is still possible to provide common boot params to override this
-	  config.
+	  Choose the type of IOMMU domain used to manage DMA API usage by
+	  device drivers. The options here typically represent different
+	  levels of tradeoff between robustness/security and performance,
+	  depending on the IOMMU driver. Not all IOMMUs support all options.
+	  This choice can be overridden at boot via the command line, and for
+	  some devices also at runtime via sysfs.
 
 	  If unsure, keep the default.
 
-config IOMMU_DEFAULT_STRICT
-	bool "strict"
+config IOMMU_DEFAULT_DMA_STRICT
+	bool "Translated - Strict"
 	help
-	  For every IOMMU DMA unmap operation, the flush operation of IOTLB and
-	  the free operation of IOVA are guaranteed to be done in the unmap
-	  function.
+	  Trusted devices use translation to restrict their access to only
+	  DMA-mapped pages, with strict TLB invalidation on unmap. Equivalent
+	  to passing "iommu.passthrough=0 iommu.strict=1" on the command line.
 
-config IOMMU_DEFAULT_LAZY
-	bool "lazy"
+	  Untrusted devices always use this mode, with an additional layer of
+	  bounce-buffering such that they cannot gain access to any unrelated
+	  data within a mapped page.
+
+config IOMMU_DEFAULT_DMA_LAZY
+	bool "Translated - Lazy"
 	help
-	  Support lazy mode, where for every IOMMU DMA unmap operation, the
-	  flush operation of IOTLB and the free operation of IOVA are deferred.
-	  They are only guaranteed to be done before the related IOVA will be
-	  reused.
+	  Trusted devices use translation to restrict their access to only
+	  DMA-mapped pages, but with "lazy" batched TLB invalidation. This
+	  mode allows higher performance with some IOMMUs due to reduced TLB
+	  flushing, but at the cost of reduced isolation since devices may be
+	  able to access memory for some time after it has been unmapped.
+	  Equivalent to passing "iommu.passthrough=0 iommu.strict=0" on the
+	  command line.
 
-	  The isolation provided in this mode is not as secure as STRICT mode,
-	  such that a vulnerable time window may be created between the DMA
-	  unmap and the mappings cached in the IOMMU IOTLB or device TLB
-	  finally being invalidated, where the device could still access the
-	  memory which has already been unmapped by the device driver.
-	  However this mode may provide better performance in high throughput
-	  scenarios, and is still considerably more secure than passthrough
-	  mode or no IOMMU.
+	  If this mode is not supported by the IOMMU driver, the effective
+	  runtime default will fall back to IOMMU_DEFAULT_DMA_STRICT.
+
+config IOMMU_DEFAULT_PASSTHROUGH
+	bool "Passthrough"
+	help
+	  Trusted devices are identity-mapped, giving them unrestricted access
+	  to memory with minimal performance overhead. Equivalent to passing
+	  "iommu.passthrough=1" (historically "iommu=pt") on the command line.
+
+	  If this mode is not supported by the IOMMU driver, the effective
+	  runtime default will fall back to IOMMU_DEFAULT_DMA_STRICT.
 
 endchoice
 
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 63face36fc49..480ad6a538a9 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -31,7 +31,7 @@ static struct kset *iommu_group_kset;
 static DEFINE_IDA(iommu_group_ida);
 
 static unsigned int iommu_def_domain_type __read_mostly;
-static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
+static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_DMA_STRICT);
 static u32 iommu_cmd_line __read_mostly;
 
 struct iommu_group {
-- 
2.25.1


  parent reply	other threads:[~2021-08-04 17:17 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-04 17:15 [PATCH v3 00/25] iommu: Refactor DMA domain strictness Robin Murphy
2021-08-04 17:15 ` [PATCH v3 01/25] iommu: Pull IOVA cookie management into the core Robin Murphy
2021-08-04 18:52   ` Heiko Stübner
2021-08-05  7:18   ` Marek Szyprowski
2021-08-05  9:15   ` Yoshihiro Shimoda
2021-08-04 17:15 ` [PATCH v3 02/25] iommu/amd: Drop IOVA cookie management Robin Murphy
2021-08-05  7:37   ` kernel test robot
2021-08-05  9:37   ` Robin Murphy
2021-08-04 17:15 ` [PATCH v3 03/25] iommu/arm-smmu: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 04/25] iommu/vt-d: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 05/25] iommu/exynos: " Robin Murphy
2021-08-05  7:19   ` Marek Szyprowski
2021-08-04 17:15 ` [PATCH v3 06/25] iommu/ipmmu-vmsa: " Robin Murphy
2021-08-05  9:15   ` Yoshihiro Shimoda
2021-08-04 17:15 ` [PATCH v3 07/25] iommu/mtk: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 08/25] iommu/rockchip: " Robin Murphy
2021-08-04 18:53   ` Heiko Stübner
2021-08-04 17:15 ` [PATCH v3 09/25] iommu/sprd: " Robin Murphy
2021-08-06  2:15   ` Chunyan Zhang
2021-08-04 17:15 ` [PATCH v3 10/25] iommu/sun50i: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 11/25] iommu/virtio: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 12/25] iommu/dma: Unexport " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 13/25] iommu/dma: Remove redundant "!dev" checks Robin Murphy
2021-08-04 17:15 ` [PATCH v3 14/25] iommu: Indicate queued flushes via gather data Robin Murphy
2021-08-04 17:15 ` [PATCH v3 15/25] iommu/io-pgtable: Remove non-strict quirk Robin Murphy
2021-08-04 17:15 ` [PATCH v3 16/25] iommu: Introduce explicit type for non-strict DMA domains Robin Murphy
2021-08-04 17:15 ` [PATCH v3 17/25] iommu/amd: Prepare for multiple DMA domain types Robin Murphy
2021-08-04 17:15 ` [PATCH v3 18/25] iommu/arm-smmu: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 19/25] iommu/vt-d: " Robin Murphy
2021-08-04 17:15 ` [PATCH v3 20/25] iommu: Express DMA strictness via the domain type Robin Murphy
2021-08-04 17:15 ` [PATCH v3 21/25] iommu: Expose DMA domain strictness via sysfs Robin Murphy
2021-08-04 17:15 ` [PATCH v3 22/25] iommu: Only log strictness for DMA domains Robin Murphy
2021-08-04 17:15 ` Robin Murphy [this message]
2021-08-06  9:15   ` [PATCH v3 23/25] iommu: Merge strictness and domain type configs John Garry
2021-08-04 17:15 ` [PATCH v3 24/25] iommu/dma: Factor out flush queue init Robin Murphy
2021-08-09 12:52   ` Will Deacon
2021-08-09 14:47     ` Robin Murphy
2021-08-09 19:05   ` Rajat Jain
2021-08-09 19:59     ` Robin Murphy
2021-08-09 20:15       ` Rajat Jain
2021-08-04 17:15 ` [PATCH v3 25/25] iommu: Allow enabling non-strict mode dynamically Robin Murphy
2021-08-09 12:49   ` Will Deacon
2021-08-09 13:40     ` Robin Murphy

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