Re: [PATCH 06/11] iommu: Expose group variants of dma ownership interfaces

On Mon, Nov 15, 2021 at 10:05:47AM +0800, Lu Baolu wrote:

The vfio needs to set DMA_OWNER_USER for the entire group when attaching

The vfio subsystem?  driver?

it to a vfio container. So expose group variants of setting/releasing dma
ownership for this purpose.

This also exposes the helper iommu_group_dma_owner_unclaimed() for vfio
report to userspace if the group is viable to user assignment, for

.. for vfio to report .. ?

 void iommu_device_release_dma_owner(struct device *dev, enum iommu_dma_owner owner);
+int iommu_group_set_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner,
+			      struct file *user_file);
+void iommu_group_release_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner);

Pleae avoid all these overly long lines.

+static inline int iommu_group_set_dma_owner(struct iommu_group *group,
+					    enum iommu_dma_owner owner,
+					    struct file *user_file)
+{
+	return -EINVAL;
+}
+
+static inline void iommu_group_release_dma_owner(struct iommu_group *group,
+						 enum iommu_dma_owner owner)
+{
+}
+
+static inline bool iommu_group_dma_owner_unclaimed(struct iommu_group *group)
+{
+	return false;
+}

Why do we need these stubs?  All potential callers should already
require CONFIG_IOMMU_API?  Same for the helpers added in patch 1, btw.

+	mutex_lock(&group->mutex);
+	ret = __iommu_group_set_dma_owner(group, owner, user_file);
+	mutex_unlock(&group->mutex);

+	mutex_lock(&group->mutex);
+	__iommu_group_release_dma_owner(group, owner);
+	mutex_unlock(&group->mutex);

Unless I'm missing something (just skipping over the patches),
the existing callers also take the lock just around these calls,
so we don't really need the __-prefixed lowlevel helpers.

+	mutex_lock(&group->mutex);
+	owner = group->dma_owner;
+	mutex_unlock(&group->mutex);

No need for a lock to read a single scalar.

+
+	return owner == DMA_OWNER_NONE;
+}
+EXPORT_SYMBOL_GPL(iommu_group_dma_owner_unclaimed);