[PATCH v7 4/6] iommu: Add bootup option "iommu.non_strict"

From: Zhen Lei <redacted>

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 <redacted>
[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);
+		}