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

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