On Thu, Jan 06, 2022 at 10:20:46AM +0800, Lu Baolu wrote:
> Expose an interface to replace the domain of an iommu group for frameworks
> like vfio which claims the ownership of the whole iommu group.
>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> include/linux/iommu.h | 10 ++++++++++
> drivers/iommu/iommu.c | 37 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 47 insertions(+)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 408a6d2b3034..66ebce3d1e11 100644
> +++ b/include/linux/iommu.h
> @@ -677,6 +677,9 @@ void iommu_device_unuse_dma_api(struct device *dev);
> int iommu_group_set_dma_owner(struct iommu_group *group, void *owner);
> void iommu_group_release_dma_owner(struct iommu_group *group);
> bool iommu_group_dma_owner_claimed(struct iommu_group *group);
> +int iommu_group_replace_domain(struct iommu_group *group,
> + struct iommu_domain *old,
> + struct iommu_domain *new);
>
> #else /* CONFIG_IOMMU_API */
>
> @@ -1090,6 +1093,13 @@ static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
> {
> return false;
> }
> +
> +static inline int
> +iommu_group_replace_domain(struct iommu_group *group, struct iommu_domain *old,
> + struct iommu_domain *new)
> +{
> + return -ENODEV;
> +}
> #endif /* CONFIG_IOMMU_API */
>
> /**
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 72a95dea688e..ab8ab95969f5 100644
> +++ b/drivers/iommu/iommu.c
> @@ -3431,3 +3431,40 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group)
> return user;
> }
> EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
> +
> +/**
> + * iommu_group_replace_domain() - Replace group's domain
> + * @group: The group.
> + * @old: The previous attached domain. NULL for none.
> + * @new: The new domain about to be attached.
> + *
> + * This is to support backward compatibility for vfio which manages the dma
> + * ownership in iommu_group level.
This should mention it can only be used with iommu_group_set_dma_owner()
> + if (old)
> + __iommu_detach_group(old, group);
> +
> + if (new) {
> + ret = __iommu_attach_group(new, group);
> + if (ret && old)
> + __iommu_attach_group(old, group);
> + }
The sketchy error unwind here gives me some pause for sure. Maybe we
should define that on error this leaves the domain as NULL
Complicates vfio a tiny bit to cope with this failure but seems
cleaner than leaving it indeterminate.
Jason
