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

Jean-Philippe Brucker
2022-05-03T18:08:00Z

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@linux.intel.com>

Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

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
>