On 2021-06-11 13:20, John Garry wrote:
From: Zhen Lei <thunder.leiz...@huawei.com>
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.leiz...@huawei.com>
Signed-off-by: John Garry <john.ga...@huawei.com>
---
drivers/iommu/Kconfig | 38 ++++++++++++++++++++++++++++++++++++++
drivers/iommu/iommu.c | 3 ++-
2 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 1f111b399bca..2a71347611d4 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -90,6 +90,44 @@ config IOMMU_DEFAULT_PASSTHROUGH
If unsure, say N here.
+choice
+ prompt "IOMMU default DMA mode"
+ depends on IOMMU_DMA
+
+ default IOMMU_DEFAULT_STRICT
+ help
+ This option allows an IOMMU DMA mode to be chosen at build time, to
+ override the default DMA mode of each ARCH, removing the need to
+ pass in kernel parameters through command line. It is still possible
+ to provide ARCH-specific or common boot options to override this
+ option.
+
+ 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 mapping finally being torn down in the IOMMU, where the
+ device can still access the system memory. 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 cf58949cc2f3..ccbd5d4c1a50 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -29,7 +29,8 @@ 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);
Nit: I reckon this is a fine place to wield the 100-character
relaxation, but it's not my call in the end.
With the wording tweaks already mentioned,
Reviewed-by: Robin Murphy <robin.mur...@arm.com>
static u32 iommu_cmd_line __read_mostly;
struct iommu_group {
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