Re: [PATCH v5 03/12] iommu: Add attach/detach_dev_pasid domain ops

[Jean-Philippe Brucker]

On Mon, May 02, 2022 at 09:48:33AM +0800, Lu Baolu wrote:
> 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 (Shared Virtual Address)
>  - kernel DMA with PASID
>  - hardware-assist mediated device
> 
> This adds a pair of common domain ops for this purpose and adds helpers
> to attach/detach a domain to/from a {device, PASID}. Some buses, like
> PCI, route packets without considering the PASID value. Thus a DMA target
> address with PASID might be treated as P2P if the address falls into the
> MMIO BAR of other devices in the group. To make things simple, these
> interfaces only apply to devices belonging to the singleton groups, and
> the singleton is immutable in fabric i.e. not affected by hotplug.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

Reviewed-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>

just a nit below

> ---
>  include/linux/iommu.h | 21 ++++++++++++
>  drivers/iommu/iommu.c | 76 +++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 97 insertions(+)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index b8ffaf2cb1d0..ab36244d4e94 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -263,6 +263,8 @@ 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.
> @@ -283,6 +285,10 @@ 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 pasid);
> +	void (*detach_dev_pasid)(struct iommu_domain *domain,
> +				 struct device *dev, ioasid_t pasid);
>  
>  	int (*map)(struct iommu_domain *domain, unsigned long iova,
>  		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
> @@ -678,6 +684,10 @@ 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 {};
> @@ -1051,6 +1061,17 @@ 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 29906bc16371..89c9d19ddb28 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -38,6 +38,7 @@ struct iommu_group {
>  	struct kobject kobj;
>  	struct kobject *devices_kobj;
>  	struct list_head devices;
> +	struct xarray pasid_array;
>  	struct mutex mutex;
>  	void *iommu_data;
>  	void (*iommu_data_release)(void *iommu_data);
> @@ -630,6 +631,7 @@ struct iommu_group *iommu_group_alloc(void)
>  	mutex_init(&group->mutex);
>  	INIT_LIST_HEAD(&group->devices);
>  	INIT_LIST_HEAD(&group->entry);
> +	xa_init(&group->pasid_array);
>  
>  	ret = ida_simple_get(&iommu_group_ida, 0, 0, GFP_KERNEL);
>  	if (ret < 0) {
> @@ -3190,3 +3192,77 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group)
>  	return user;
>  }
>  EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
> +
> +/*
> + * Use standard PCI bus topology and isolation features to check immutable
> + * singleton. Otherwise, assume the bus is static and then singleton can
> + * know from the device count in the group.
> + */

The comment doesn't really add anything that can't be directly understood
from the code.

> +static bool device_group_immutable_singleton(struct device *dev)
> +{
> +	struct iommu_group *group = iommu_group_get(dev);
> +	int count;
> +
> +	if (!group)
> +		return false;
> +
> +	mutex_lock(&group->mutex);
> +	count = iommu_group_device_count(group);
> +	mutex_unlock(&group->mutex);
> +	iommu_group_put(group);
> +
> +	if (count != 1)
> +		return false;
> +
> +	/*
> +	 * The PCI device could be considered to be fully isolated if all
> +	 * devices on the path from the device to the host-PCI bridge are
> +	 * protected from peer-to-peer DMA by ACS.
> +	 */
> +	if (dev_is_pci(dev))
> +		return pci_acs_path_enabled(to_pci_dev(dev), NULL,
> +					    REQ_ACS_FLAGS);
> +
> +	return true;
> +}
> +
> +int iommu_attach_device_pasid(struct iommu_domain *domain,
> +			      struct device *dev, ioasid_t pasid)
> +{
> +	struct iommu_group *group;
> +	int ret = -EINVAL;
> +	void *curr;
> +
> +	if (!domain->ops->attach_dev_pasid)
> +		return -EOPNOTSUPP;
> +
> +	if (!device_group_immutable_singleton(dev))
> +		return -EINVAL;
> +
> +	group = iommu_group_get(dev);
> +	mutex_lock(&group->mutex);
> +	curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, GFP_KERNEL);
> +	if (curr)
> +		goto out_unlock;
> +	ret = domain->ops->attach_dev_pasid(domain, dev, pasid);
> +	if (ret)
> +		xa_erase(&group->pasid_array, 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 = iommu_group_get(dev);
> +
> +	mutex_lock(&group->mutex);
> +	domain->ops->detach_dev_pasid(domain, dev, pasid);
> +	xa_erase(&group->pasid_array, pasid);
> +	mutex_unlock(&group->mutex);
> +
> +	iommu_group_put(group);
> +}
> -- 
> 2.25.1
>