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 <j...@8bytes.org> Reviewed-by: Lu Baolu <baolu...@linux.intel.com> Reviewed-by: Jean-Philippe Brucker <jean-phili...@linaro.org> Signed-off-by: Robin Murphy <robin.mur...@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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu