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Subject[PATCH v6 7/7] iommu/dma: Add bootup option "iommu.non_strict"
Date
From: Zhen Lei <thunder.leizhen@huawei.com>

Add a bootup option to make the system manager can choose which mode to
be used. The default mode is strict.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: make it a generic iommu-dma feature]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
.../admin-guide/kernel-parameters.txt | 13 +++++++++++++
drivers/iommu/dma-iommu.c | 18 ++++++++++++++++++
2 files changed, 31 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..406b91759b62 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1749,6 +1749,19 @@
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.

+ iommu.non_strict= [ARM64]
+ Format: { "0" | "1" }
+ 0 - strict mode, default.
+ Release IOVAs after the related TLBs are invalid
+ completely.
+ 1 - non-strict mode.
+ Put off TLBs invalidation and release memory first.
+ It's good for scatter-gather performance but lacks
+ full isolation, an untrusted device can access the
+ reused memory because the TLBs may still valid.
+ Please take full consideration before choosing this
+ mode. Note that, VFIO will always use strict mode.
+
iommu.passthrough=
[ARM64] Configure DMA to bypass the IOMMU by default.
Format: { "0" | "1" }
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index d91849fe4ebe..04d4c5453acd 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -62,6 +62,24 @@ struct iommu_dma_cookie {

static bool iommu_dma_non_strict __read_mostly;

+static int __init iommu_dma_setup(char *str)
+{
+ int ret;
+
+ ret = kstrtobool(str, &iommu_dma_non_strict);
+ if (ret)
+ return ret;
+
+ if (iommu_dma_non_strict) {
+ pr_warn("WARNING: iommu non-strict mode is chosen.\n"
+ "It's good for scatter-gather performance but lacks full isolation\n");
+ add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
+ }
+
+ return 0;
+}
+early_param("iommu.non_strict", iommu_dma_setup);
+
static inline size_t cookie_msi_granule(struct iommu_dma_cookie *cookie)
{
if (cookie->type == IOMMU_DMA_IOVA_COOKIE)
--
2.19.0.dirty
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