iommu: Merge strictness and domain type configs

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>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/d04af35b9c0f2a1d39605d7a9b451f5e1f0c7736.1628682049.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 90b525c..19192b3 100644 (file)
--- 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 c84da82..6e06f87 100644 (file)
--- 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"
+choice
+       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
-         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.
+         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, say N here.
+         If unsure, keep the default.
 
-choice
-       prompt "IOMMU default DMA IOTLB invalidation mode"
-       depends on IOMMU_DMA
+config IOMMU_DEFAULT_DMA_STRICT
+       bool "Translated - Strict"
+       help
+         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.
 
-       default IOMMU_DEFAULT_LAZY if (AMD_IOMMU || INTEL_IOMMU)
-       default IOMMU_DEFAULT_STRICT
+         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
-         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.
+         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.
 
-         If unsure, keep the default.
+         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.
 
-config IOMMU_DEFAULT_STRICT
-       bool "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.
-
-config IOMMU_DEFAULT_LAZY
-       bool "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.
-
-         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.
 
 endchoice
 

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 069f7dc..0e1f791 100644 (file)
--- 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 {