[PATCH v8 3/7] iommu: Add "iommu.strict" command line option

From: Zhen Lei <redacted>

Add a generic command line option to enable lazy unmapping via IOVA
flush queues, which will initally be suuported by iommu-dma. This echoes
the semantics of "intel_iommu=strict" (albeit with the opposite default
value), but in the driver-agnostic fashion of "iommu.passthrough".

Signed-off-by: Zhen Lei <redacted>
[rm: move handling out of SMMUv3 driver, clean up documentation]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

v8:
 - Rename "non-strict" to "strict" to better match existing options
 - Rewrite doc text/commit message
 - Downgrade boot-time message from warn/taint to info

 .../admin-guide/kernel-parameters.txt         | 12 ++++++++++
 drivers/iommu/iommu.c                         | 23 +++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..92ae12aeabf4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt

@@ -1749,6 +1749,18 @@
 		nobypass	[PPC/POWERNV]
 			Disable IOMMU bypass, using IOMMU for PCI devices.
 
+	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
+			Format: { "0" | "1" }
+			0 - Lazy mode.
+			  Request that DMA unmap operations use deferred
+			  invalidation of hardware TLBs, for increased
+			  throughput at the cost of reduced device isolation.
+			  Will fall back to strict mode if not supported by
+			  the relevant IOMMU driver.
+			1 - Strict mode (default).
+			  DMA unmap operations invalidate IOMMU hardware TLBs
+			  synchronously.
+
 	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..02b6603f0616 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_strict __read_mostly = true;
 
 struct iommu_callback_data {
 	const struct iommu_ops *ops;

@@ -131,6 +132,21 @@ 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_strict);
+	if (ret)
+		return ret;
+
+	if (!iommu_dma_strict)
+		pr_info("Enabling deferred TLB invalidation for DMA; protection against malicious/malfunctioning devices may be reduced.\n");