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Subject[PATCH v4 5/5] iommu/arm-smmu-v3: add bootup option "arm_iommu"
Date
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>
---
Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
drivers/iommu/arm-smmu-v3.c | 17 ++++++++++++++++-
2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 533ff5c..426e989 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1720,6 +1720,15 @@
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.

+ arm_iommu= [ARM64]
+ non-strict [Default Off]
+ 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/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 904bc1e..9a30892 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -631,6 +631,21 @@ struct arm_smmu_option_prop {
{ 0, NULL},
};

+static u32 smmu_non_strict __read_mostly;
+
+static int __init arm_smmu_setup(char *str)
+{
+ if (!strncmp(str, "non-strict", 10)) {
+ smmu_non_strict = 1;
+ 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("arm_iommu", arm_smmu_setup);
+
static inline void __iomem *arm_smmu_page1_fixup(unsigned long offset,
struct arm_smmu_device *smmu)
{
@@ -1622,7 +1637,7 @@ static int arm_smmu_domain_finalise(struct iommu_domain *domain)
if (smmu->features & ARM_SMMU_FEAT_COHERENCY)
pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA;

- if (domain->type == IOMMU_DOMAIN_DMA) {
+ if ((domain->type == IOMMU_DOMAIN_DMA) && smmu_non_strict) {
domain->non_strict = 1;
pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
}
--
1.8.3

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