Re: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev()

Alex Williamson
2020-07-29T20:25:20Z

On Tue, 14 Jul 2020 13:57:02 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> The device driver needs an API to get its aux-domain. A typical usage
> scenario is:
>
> unsigned long pasid;
> struct iommu_domain *domain;
> struct device *dev = mdev_dev(mdev);
> struct device *iommu_device = vfio_mdev_get_iommu_device(dev);
>
> domain = iommu_aux_get_domain_for_dev(dev);
> if (!domain)
> return -ENODEV;
>
> pasid = iommu_aux_get_pasid(domain, iommu_device);
> if (pasid <= 0)
> return -EINVAL;
>
> /* Program the device context */
> ....
>
> This adds an API for such use case.
>
> Suggested-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
> drivers/iommu/iommu.c | 18 ++++++++++++++++++
> include/linux/iommu.h | 7 +++++++
> 2 files changed, 25 insertions(+)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index cad5a19ebf22..434bf42b6b9b 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2817,6 +2817,24 @@ void iommu_aux_detach_group(struct iommu_domain *domain,
> }
> EXPORT_SYMBOL_GPL(iommu_aux_detach_group);
>
> +struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev)
> +{
> + struct iommu_domain *domain = NULL;
> + struct iommu_group *group;
> +
> + group = iommu_group_get(dev);
> + if (!group)
> + return NULL;
> +
> + if (group->aux_domain_attached)
> + domain = group->domain;

Why wouldn't the aux domain flag be on the domain itself rather than
the group? Then if we wanted sanity checking in patch 1/ we'd only
need to test the flag on the object we're provided.

If we had such a flag, we could create an iommu_domain_is_aux()
function and then simply use iommu_get_domain_for_dev() and test that
it's an aux domain in the example use case. It seems like that would
resolve the jump from a domain to an aux-domain just as well as adding
this separate iommu_aux_get_domain_for_dev() interface. The is_aux
test might also be useful in other cases too. Thanks,

Alex

> +
> + iommu_group_put(group);
> +
> + return domain;
> +}
> +EXPORT_SYMBOL_GPL(iommu_aux_get_domain_for_dev);
> +
> /**
> * iommu_sva_bind_device() - Bind a process address space to a device
> * @dev: the device
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9506551139ab..cda6cef7579e 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -639,6 +639,7 @@ int iommu_aux_attach_group(struct iommu_domain *domain,
> struct iommu_group *group, struct device *dev);
> void iommu_aux_detach_group(struct iommu_domain *domain,
> struct iommu_group *group, struct device *dev);
> +struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev);
>
> struct iommu_sva *iommu_sva_bind_device(struct device *dev,
> struct mm_struct *mm,
> @@ -1040,6 +1041,12 @@ iommu_aux_detach_group(struct iommu_domain *domain,
> {
> }
>
> +static inline struct iommu_domain *
> +iommu_aux_get_domain_for_dev(struct device *dev)
> +{
> + return NULL;
> +}
> +
> static inline struct iommu_sva *
> iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void *drvdata)
> {