iommu: Add "iommu.strict" command line option

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 <thunder.leizhen@huawei.com>
[rm: move handling out of SMMUv3 driver, clean up documentation]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
[will: dropped broken printk when parsing command-line option]
Signed-off-by: Will Deacon <will.deacon@arm.com>

2 files changed, 26 insertions, 0 deletions

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..2b6dad2aa9f1 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 +132,12 @@ 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)
+{
+        return kstrtobool(str, &iommu_dma_strict);
+}
+early_param("iommu.strict", iommu_dma_setup);
+
 static ssize_t iommu_group_attr_show(struct kobject *kobj,
                                      struct attribute *__attr, char *buf)
 {
@@ -1072,6 +1079,13 @@ 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_strict) {
+                        int attr = 1;
+                        iommu_domain_set_attr(dom,
+                                              DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
+                                              &attr);
+                }
         }
 
         ret = iommu_group_add_device(group, dev);