[PATCH v2 11/17] iommu: Add iommu_at[de]tach_device_shared() for multi-device groups

[Lu Baolu]

The iommu_attach/detach_device() interfaces were exposed for the device
drivers to attach/detach their own domains. The commit <426a273834eae>
("iommu: Limit iommu_attach/detach_device to device with their own group")
restricted them to singleton groups to avoid different device in a group
attaching different domain.

As we've introduced device DMA ownership into the iommu core. We can now
introduce interfaces for muliple-device groups, and "all devices are in the
same address space" is still guaranteed.

The iommu_attach/detach_device_shared() could be used when multiple drivers
sharing the group claim the DMA_OWNER_PRIVATE_DOMAIN ownership. The first
call of iommu_attach_device_shared() attaches the domain to the group.
Other drivers could join it later. The domain will be detached from the
group after all drivers unjoin it.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 include/linux/iommu.h | 13 +++++++++
 drivers/iommu/iommu.c | 61 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index afcc07bc8d41..8c81ba11ae8c 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -705,6 +705,8 @@ int iommu_group_set_dma_owner(struct iommu_group *group, enum iommu_dma_owner ow
 			      void *owner_cookie);
 void iommu_group_release_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner);
 bool iommu_group_dma_owner_unclaimed(struct iommu_group *group);
+int iommu_attach_device_shared(struct iommu_domain *domain, struct device *dev);
+void iommu_detach_device_shared(struct iommu_domain *domain, struct device *dev);
 
 #else /* CONFIG_IOMMU_API */
 
@@ -745,11 +747,22 @@ static inline int iommu_attach_device(struct iommu_domain *domain,
 	return -ENODEV;
 }
 
+static inline int iommu_attach_device_shared(struct iommu_domain *domain,
+					     struct device *dev)
+{
+	return -ENODEV;
+}
+
 static inline void iommu_detach_device(struct iommu_domain *domain,
 				       struct device *dev)
 {
 }
 
+static inline void iommu_detach_device_shared(struct iommu_domain *domain,
+					      struct device *dev)
+{
+}
+
 static inline struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)
 {
 	return NULL;
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 423197db99a9..f9cb96acbac8 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -50,6 +50,7 @@ struct iommu_group {
 	struct list_head entry;
 	enum iommu_dma_owner dma_owner;
 	refcount_t owner_cnt;
+	refcount_t attach_cnt;
 	void *owner_cookie;
 };
 
@@ -2026,6 +2027,41 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
 }
 EXPORT_SYMBOL_GPL(iommu_attach_device);
 
+int iommu_attach_device_shared(struct iommu_domain *domain, struct device *dev)
+{
+	struct iommu_group *group;
+	int ret = 0;
+
+	group = iommu_group_get(dev);
+	if (!group)
+		return -ENODEV;
+
+	mutex_lock(&group->mutex);
+	if (refcount_inc_not_zero(&group->attach_cnt)) {
+		if (group->domain != domain ||
+		    (group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN &&
+		     group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN_USER)) {
+			refcount_dec(&group->attach_cnt);
+			ret = -EBUSY;
+		}
+
+		goto unlock_out;
+	}
+
+	ret = __iommu_attach_group(domain, group);
+	if (ret)
+		goto unlock_out;
+
+	refcount_set(&group->owner_cnt, 1);
+
+unlock_out:
+	mutex_unlock(&group->mutex);
+	iommu_group_put(group);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iommu_attach_device_shared);
+
 int iommu_deferred_attach(struct device *dev, struct iommu_domain *domain)
 {
 	const struct iommu_ops *ops = domain->ops;
@@ -2281,6 +2317,31 @@ void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
 }
 EXPORT_SYMBOL_GPL(iommu_detach_device);
 
+void iommu_detach_device_shared(struct iommu_domain *domain, struct device *dev)
+{
+	struct iommu_group *group;
+
+	group = iommu_group_get(dev);
+	if (!group)
+		return;
+
+	mutex_lock(&group->mutex);
+	if (WARN_ON(group->domain != domain ||
+		    (group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN &&
+		     group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN_USER)))
+		goto unlock_out;
+
+	if (refcount_dec_and_test(&group->owner_cnt)) {
+		__iommu_detach_group(domain, group);
+		group->dma_owner = DMA_OWNER_NONE;
+	}
+
+unlock_out:
+	mutex_unlock(&group->mutex);
+	iommu_group_put(group);
+}
+EXPORT_SYMBOL_GPL(iommu_detach_device_shared);
+
 struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)
 {
 	struct iommu_domain *domain;
-- 
2.25.1