iommu: Enhance IOMMU default DMA mode build options

First, add build options IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
opportunity to set {lazy|strict} mode as default at build time. Then put
the two config options in an choice, as they are mutually exclusive.

[jpg: Make choice between strict and lazy only (and not passthrough)]

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/1626088340-5838-4-git-send-email-john.garry@huawei.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 a04d274..90b525c 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2042,9 +2042,10 @@
                          throughput at the cost of reduced device isolation.
                          Will fall back to strict mode if not supported by
                          the relevant IOMMU driver.
-                       1 - Strict mode (default).
+                       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

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 07b7c25..9cd5d7a 100644 (file)
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -90,6 +90,46 @@ config IOMMU_DEFAULT_PASSTHROUGH
 
          If unsure, say N here.
 
+choice
+       prompt "IOMMU default DMA IOTLB invalidation mode"
+       depends on IOMMU_DMA
+
+       default IOMMU_DEFAULT_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.
+
+         If unsure, keep the default.
+
+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.
+
+endchoice
+
 config OF_IOMMU
        def_bool y
        depends on OF && IOMMU_API

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 69d7d48..bd9ccce 100644 (file)
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -30,7 +30,7 @@ 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 = true;
+static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
 static u32 iommu_cmd_line __read_mostly;
 
 struct iommu_group {