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Subject[PATCH v7 4/6] iommu: 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: move handling out of SMMUv3 driver]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
.../admin-guide/kernel-parameters.txt | 13 ++++++++++
drivers/iommu/iommu.c | 26 +++++++++++++++++++
2 files changed, 39 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/iommu.c b/drivers/iommu/iommu.c
index 8c15c5980299..2cabd0c0a4f3 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -41,6 +41,7 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY;
#else
static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
#endif
+static bool iommu_dma_non_strict __read_mostly;

struct iommu_callback_data {
const struct iommu_ops *ops;
@@ -131,6 +132,24 @@ static int __init iommu_set_def_domain_type(char *str)
}
early_param("iommu.passthrough", iommu_set_def_domain_type);

+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 ssize_t iommu_group_attr_show(struct kobject *kobj,
struct attribute *__attr, char *buf)
{
@@ -1072,6 +1091,13 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
group->default_domain = dom;
if (!group->domain)
group->domain = dom;
+
+ if (dom && iommu_dma_non_strict) {
+ int attr = 1;
+ iommu_domain_set_attr(dom,
+ DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
+ &attr);
+ }
}

ret = iommu_group_add_device(group, dev);
--
2.19.0.dirty
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