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

Christoph Hellwig
2021-11-15T13:28:03Z

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);