Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()

[Robin Murphy <robin.murphy@arm.com>]

On 2022-01-06 02:20, 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.

But if the underlying point is the new expectation that 
iommu_{attach,detach}_device() operate on the device's whole group where 
relevant, why should we invent some special mechanism for VFIO to be 
needlessly inconsistent?

I said before that it's trivial for VFIO to resolve a suitable device if 
it needs to; by now I've actually written the patch ;)

https://gitlab.arm.com/linux-arm/linux-rm/-/commit/9f37d8c17c9b606abc96e1f1001c0b97c8b93ed5

Robin.

> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>   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
> --- a/include/linux/iommu.h
> +++ 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
> --- a/drivers/iommu/iommu.c
> +++ 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.
> + */
> +int iommu_group_replace_domain(struct iommu_group *group,
> +			       struct iommu_domain *old,
> +			       struct iommu_domain *new)
> +{
> +	int ret = 0;
> +
> +	mutex_lock(&group->mutex);
> +	if (!group->owner || group->domain != old) {
> +		ret = -EPERM;
> +		goto unlock_out;
> +	}
> +
> +	if (old)
> +		__iommu_detach_group(old, group);
> +
> +	if (new) {
> +		ret = __iommu_attach_group(new, group);
> +		if (ret && old)
> +			__iommu_attach_group(old, group);
> +	}
> +
> +unlock_out:
> +	mutex_unlock(&group->mutex);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_group_replace_domain);