[PATCH v4 7/7] iommu/dma: Add IOMMU op to choose lazy domain type

[Niklas Schnelle]

With two flush queue variants add an IOMMU operation that allows the
IOMMU driver to choose its preferred flush queue variant on a per device
basis. For s390 use this callback to choose the single queue variant
whenever the device requires explicit IOTLB flushes on map indicating
that we're running in a paged memory guest with expensive IOTLB flushes.

Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
 drivers/iommu/iommu.c      | 13 +++++++++++++
 drivers/iommu/s390-iommu.c | 11 +++++++++++
 include/linux/iommu.h      |  5 +++++
 3 files changed, 29 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 7ae2ff35b88e..c4699a0e5feb 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1616,6 +1616,16 @@ static int iommu_get_def_domain_type(struct device *dev)
 	return 0;
 }
 
+static int iommu_get_lazy_domain_type(struct device *dev)
+{
+	const struct iommu_ops *ops = dev_iommu_ops(dev);
+
+	if (ops->lazy_domain_type)
+		return ops->lazy_domain_type(dev);
+
+	return 0;
+}
+
 static int iommu_group_alloc_default_domain(struct bus_type *bus,
 					    struct iommu_group *group,
 					    unsigned int type)
@@ -1649,6 +1659,9 @@ static int iommu_alloc_default_domain(struct iommu_group *group,
 
 	type = iommu_get_def_domain_type(dev) ? : iommu_def_domain_type;
 
+	if (!!(type & __IOMMU_DOMAIN_DMA_LAZY))
+		type = iommu_get_lazy_domain_type(dev) ? : type;
+
 	return iommu_group_alloc_default_domain(dev->bus, group, type);
 }
 
diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index ff73b75be886..b8aab37e8b15 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -459,6 +459,16 @@ static void s390_iommu_get_resv_regions(struct device *dev,
 	}
 }
 
+static int s390_iommu_lazy_domain_type(struct device *dev)
+{
+	struct zpci_dev *zdev = to_zpci_dev(dev);
+
+	if (zdev->tlb_refresh)
+		return IOMMU_DOMAIN_DMA_SQ;
+
+	return IOMMU_DOMAIN_DMA_FQ;
+}
+
 static struct iommu_device *s390_iommu_probe_device(struct device *dev)
 {
 	struct zpci_dev *zdev;
@@ -798,6 +808,7 @@ static const struct iommu_ops s390_iommu_ops = {
 	.device_group = generic_device_group,
 	.pgsize_bitmap = SZ_4K,
 	.get_resv_regions = s390_iommu_get_resv_regions,
+	.lazy_domain_type = s390_iommu_lazy_domain_type,
 	.default_domain_ops = &(const struct iommu_domain_ops) {
 		.attach_dev	= s390_iommu_attach_device,
 		.detach_dev	= s390_iommu_detach_device,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 74cee59516aa..aec895087f63 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -250,6 +250,10 @@ struct iommu_iotlb_gather {
  *		- IOMMU_DOMAIN_IDENTITY: must use an identity domain
  *		- IOMMU_DOMAIN_DMA: must use a dma domain
  *		- 0: use the default setting
+ * @lazy_domain_type: Domain type for lazy TLB invalidation, return value:
+ *		- IOMMU_DOMAIN_DMA_FQ: Use per-CPU flush queue
+ *		- IOMMU_DOMAIN_DMA_SQ: Use single flush queue
+ *		- 0: use the default setting
  * @default_domain_ops: the default ops for domains
  * @remove_dev_pasid: Remove any translation configurations of a specific
  *                    pasid, so that any DMA transactions with this pasid
@@ -283,6 +287,7 @@ struct iommu_ops {
 			     struct iommu_page_response *msg);
 
 	int (*def_domain_type)(struct device *dev);
+	int (*lazy_domain_type)(struct device *dev);
 	void (*remove_dev_pasid)(struct device *dev, ioasid_t pasid);
 
 	const struct iommu_domain_ops *default_domain_ops;
-- 
2.34.1