RE: [PATCH RFC 03/11] iommu: Add attach/detach_dev_pasid domain ops

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Sunday, March 20, 2022 2:40 PM
> 
> Attaching an IOMMU domain to a PASID of a device is a generic operation
> for modern IOMMU drivers which support PASID-granular DMA address
> translation. Currently visible usage scenarios include (but not limited):
> 
>  - SVA
>  - kernel DMA with PASID
>  - hardware-assist mediated device
> 
> This adds a pair of common domain ops for this purpose and implements a
> couple of wrapper helpers for in-kernel usage.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/iommu.h | 22 ++++++++++++++++++++++
>  drivers/iommu/iommu.c | 41
> +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 63 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 3e179b853380..e51845b9a146 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -268,6 +268,8 @@ struct iommu_ops {
>   * struct iommu_domain_ops - domain specific operations
>   * @attach_dev: attach an iommu domain to a device
>   * @detach_dev: detach an iommu domain from a device
> + * @attach_dev_pasid: attach an iommu domain to a pasid of device
> + * @detach_dev_pasid: detach an iommu domain from a pasid of device
>   * @map: map a physically contiguous memory region to an iommu domain
>   * @map_pages: map a physically contiguous set of pages of the same size
> to
>   *             an iommu domain.
> @@ -285,6 +287,10 @@ struct iommu_ops {
>  struct iommu_domain_ops {
>  	int (*attach_dev)(struct iommu_domain *domain, struct device *dev);
>  	void (*detach_dev)(struct iommu_domain *domain, struct device
> *dev);
> +	int (*attach_dev_pasid)(struct iommu_domain *domain,
> +				struct device *dev, ioasid_t id);
> +	void (*detach_dev_pasid)(struct iommu_domain *domain,
> +				 struct device *dev, ioasid_t id);
> 
>  	int (*map)(struct iommu_domain *domain, unsigned long iova,
>  		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
> @@ -678,6 +684,11 @@ int iommu_group_claim_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_attach_device_pasid(struct iommu_domain *domain,
> +			      struct device *dev, ioasid_t pasid);
> +void iommu_detach_device_pasid(struct iommu_domain *domain,
> +			       struct device *dev, ioasid_t pasid);
> +
>  #else /* CONFIG_IOMMU_API */
> 
>  struct iommu_ops {};
> @@ -1046,6 +1057,17 @@ static inline bool
> iommu_group_dma_owner_claimed(struct iommu_group *group)
>  {
>  	return false;
>  }
> +
> +static inline int iommu_attach_device_pasid(struct iommu_domain
> *domain,
> +					    struct device *dev, ioasid_t pasid)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline void iommu_detach_device_pasid(struct iommu_domain
> *domain,
> +					     struct device *dev, ioasid_t pasid)
> +{
> +}
>  #endif /* CONFIG_IOMMU_API */
> 
>  /**
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0c42ece25854..78c71ee15f36 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3167,3 +3167,44 @@ bool iommu_group_dma_owner_claimed(struct
> iommu_group *group)
>  	return user;
>  }
>  EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
> +
> +int iommu_attach_device_pasid(struct iommu_domain *domain,
> +			      struct device *dev, ioasid_t pasid)
> +{
> +	struct iommu_group *group;
> +	int ret = -EINVAL;
> +
> +	if (!domain->ops->attach_dev_pasid)
> +		return -EINVAL;
> +
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		return -ENODEV;
> +
> +	mutex_lock(&group->mutex);
> +	if (iommu_group_device_count(group) != 1)
> +		goto out_unlock;

Need move the reason of above limitation from iommu_sva_bind_device()
to here:

	/*
	 * To keep things simple, SVA currently doesn't support IOMMU groups
	 * with more than one device. Existing SVA-capable systems are not
	 * affected by the problems that required IOMMU groups (lack of ACS
	 * isolation, device ID aliasing and other hardware issues).
	 */
	if (iommu_group_device_count(group) != 1)
		goto out_unlock;

btw I didn't see any safeguard on above assumption in device hotplug path
to a group which already has SVA enabled...

> +
> +	ret = domain->ops->attach_dev_pasid(domain, dev, pasid);
> +
> +out_unlock:
> +	mutex_unlock(&group->mutex);
> +	iommu_group_put(group);
> +
> +	return ret;
> +}
> +
> +void iommu_detach_device_pasid(struct iommu_domain *domain,
> +			       struct device *dev, ioasid_t pasid)
> +{
> +	struct iommu_group *group;
> +
> +	group = iommu_group_get(dev);
> +	if (WARN_ON(!group))
> +		return;
> +
> +	mutex_lock(&group->mutex);
> +	domain->ops->detach_dev_pasid(domain, dev, pasid);
> +	mutex_unlock(&group->mutex);
> +	iommu_group_put(group);
> +}
> --
> 2.25.1