[PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev()

[Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>]

The device driver needs an API to get its aux-domain. A typical usage
scenario is:

        unsigned long pasid;
        struct iommu_domain *domain;
        struct device *dev = mdev_dev(mdev);
        struct device *iommu_device = vfio_mdev_get_iommu_device(dev);

        domain = iommu_aux_get_domain_for_dev(dev);
        if (!domain)
                return -ENODEV;

        pasid = iommu_aux_get_pasid(domain, iommu_device);
        if (pasid <= 0)
                return -EINVAL;

         /* Program the device context */
         ....

This adds an API for such use case.

Suggested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/iommu/iommu.c | 18 ++++++++++++++++++
 include/linux/iommu.h |  7 +++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index cad5a19ebf22..434bf42b6b9b 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2817,6 +2817,24 @@ void iommu_aux_detach_group(struct iommu_domain *domain,
 }
 EXPORT_SYMBOL_GPL(iommu_aux_detach_group);
 
+struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev)
+{
+	struct iommu_domain *domain = NULL;
+	struct iommu_group *group;
+
+	group = iommu_group_get(dev);
+	if (!group)
+		return NULL;
+
+	if (group->aux_domain_attached)
+		domain = group->domain;
+
+	iommu_group_put(group);
+
+	return domain;
+}
+EXPORT_SYMBOL_GPL(iommu_aux_get_domain_for_dev);
+
 /**
  * iommu_sva_bind_device() - Bind a process address space to a device
  * @dev: the device
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 9506551139ab..cda6cef7579e 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -639,6 +639,7 @@ int iommu_aux_attach_group(struct iommu_domain *domain,
 			   struct iommu_group *group, struct device *dev);
 void iommu_aux_detach_group(struct iommu_domain *domain,
 			   struct iommu_group *group, struct device *dev);
+struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev);
 
 struct iommu_sva *iommu_sva_bind_device(struct device *dev,
 					struct mm_struct *mm,
@@ -1040,6 +1041,12 @@ iommu_aux_detach_group(struct iommu_domain *domain,
 {
 }
 
+static inline struct iommu_domain *
+iommu_aux_get_domain_for_dev(struct device *dev)
+{
+	return NULL;
+}
+
 static inline struct iommu_sva *
 iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void *drvdata)
 {
-- 
2.17.1