[PATCH v4 3/5] 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>
Link: https://lore.kernel.org/linux-iommu/20200708130749.1b1e1421@xxxxxxx/
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/iommu/iommu.c | 18 ++++++++++++++++++
 include/linux/iommu.h | 20 ++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index fb21c2ff4861..8fd93a5b8764 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2893,6 +2893,24 @@ void iommu_detach_subdev_group(struct iommu_domain *domain,
 }
 EXPORT_SYMBOL_GPL(iommu_detach_subdev_group);
 
+struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *subdev)
+{
+	struct iommu_domain *domain = NULL;
+	struct iommu_group *group;
+
+	group = iommu_group_get(subdev);
+	if (!group || !group->domain)
+		return NULL;
+
+	if (domain_is_aux(group->domain, subdev))
+		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 b9df8b510d4f..ea660a887dbf 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -120,6 +120,7 @@ enum iommu_attr {
 	DOMAIN_ATTR_NESTING,	/* two stages of translation */
 	DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE,
 	DOMAIN_ATTR_MAX,
+	DOMAIN_ATTR_IS_AUX,
 };
 
 /* These are the possible reserved region types */
@@ -622,6 +623,12 @@ static inline void dev_iommu_priv_set(struct device *dev, void *priv)
 	dev->iommu->priv = priv;
 }
 
+static inline bool
+domain_is_aux(struct iommu_domain *domain, struct device *subdev)
+{
+	return iommu_domain_get_attr(domain, DOMAIN_ATTR_IS_AUX, subdev);
+}
+
 int iommu_probe_device(struct device *dev);
 void iommu_release_device(struct device *dev);
 
@@ -638,6 +645,7 @@ int iommu_attach_subdev_group(struct iommu_domain *domain,
 void iommu_detach_subdev_group(struct iommu_domain *domain,
 			       struct iommu_group *group,
 			       iommu_device_lookup_t fn);
+struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *subdev);
 
 struct iommu_sva *iommu_sva_bind_device(struct device *dev,
 					struct mm_struct *mm,
@@ -1039,6 +1047,18 @@ iommu_detach_subdev_group(struct iommu_domain *domain, struct iommu_group *group
 {
 }
 
+static inline bool
+domain_is_aux(struct iommu_domain *domain, struct device *subdev)
+{
+	return false;
+}
+
+static inline struct iommu_domain *
+iommu_aux_get_domain_for_dev(struct device *subdev)
+{
+	return NULL;
+}
+
 static inline struct iommu_sva *
 iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void *drvdata)
 {
-- 
2.17.1