Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

[Christoph Hellwig <hch@infradead.org>]

On Tue, Jan 04, 2022 at 09:56:31AM +0800, Lu Baolu wrote:
> Multiple devices may be placed in the same IOMMU group because they
> cannot be isolated from each other. These devices must either be
> entirely under kernel control or userspace control, never a mixture.
> 
> This adds dma ownership management in iommu core and exposes several
> interfaces for the device drivers and the device userspace assignment
> framework (i.e. vfio), so that any conflict between user and kernel
> controlled DMA could be detected at the beginning.
> 
> The device driver oriented interfaces are,
> 
> 	int iommu_device_use_dma_api(struct device *dev);
> 	void iommu_device_unuse_dma_api(struct device *dev);
> 
> Devices under kernel drivers control must call iommu_device_use_dma_api()
> before driver probes. The driver binding process must be aborted if it
> returns failure.
> 
> The vfio oriented interfaces are,
> 
> 	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);
> 
> The device userspace assignment must be disallowed if the set dma owner
> interface returns failure.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  include/linux/iommu.h |  31 ++++++++
>  drivers/iommu/iommu.c | 161 +++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 189 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index de0c57a567c8..568f285468cf 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -682,6 +682,13 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>  void iommu_sva_unbind_device(struct iommu_sva *handle);
>  u32 iommu_sva_get_pasid(struct iommu_sva *handle);
>  
> +int iommu_device_use_dma_api(struct device *dev);
> +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);
> +
>  #else /* CONFIG_IOMMU_API */
>  
>  struct iommu_ops {};
> @@ -1082,6 +1089,30 @@ static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
>  {
>  	return NULL;
>  }
> +
> +static inline int iommu_device_use_dma_api(struct device *dev)
> +{
> +	return 0;
> +}
> +
> +static inline void iommu_device_unuse_dma_api(struct device *dev)
> +{
> +}
> +
> +static inline int
> +iommu_group_set_dma_owner(struct iommu_group *group, void *owner)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline void iommu_group_release_dma_owner(struct iommu_group *group)
> +{
> +}
> +
> +static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
> +{
> +	return false;
> +}
>  #endif /* CONFIG_IOMMU_API */
>  
>  /**
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 8b86406b7162..ff0c8c1ad5af 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -48,6 +48,8 @@ struct iommu_group {
>  	struct iommu_domain *default_domain;
>  	struct iommu_domain *domain;
>  	struct list_head entry;
> +	unsigned int owner_cnt;
> +	void *owner;
>  };
>  
>  struct group_device {
> @@ -289,7 +291,12 @@ int iommu_probe_device(struct device *dev)
>  	mutex_lock(&group->mutex);
>  	iommu_alloc_default_domain(group, dev);
>  
> -	if (group->default_domain) {
> +	/*
> +	 * If device joined an existing group which has been claimed
> +	 * for none kernel DMA purpose, avoid attaching the default
> +	 * domain.
> +	 */
> +	if (group->default_domain && !group->owner) {
>  		ret = __iommu_attach_device(group->default_domain, dev);
>  		if (ret) {
>  			mutex_unlock(&group->mutex);
> @@ -2320,7 +2327,7 @@ static int __iommu_attach_group(struct iommu_domain *domain,
>  {
>  	int ret;
>  
> -	if (group->default_domain && group->domain != group->default_domain)
> +	if (group->domain && group->domain != group->default_domain)
>  		return -EBUSY;
>  
>  	ret = __iommu_group_for_each_dev(group, domain,
> @@ -2357,7 +2364,11 @@ static void __iommu_detach_group(struct iommu_domain *domain,
>  {
>  	int ret;
>  
> -	if (!group->default_domain) {
> +	/*
> +	 * If group has been claimed for none kernel DMA purpose, avoid
> +	 * re-attaching the default domain.
> +	 */

none kernel reads odd.  But maybe drop that and just say 'claimed
already' ala:

	/*
	 * If the group has been claimed already, do not re-attach the default
	 * domain.
	 */