linux-kernel - Re: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for

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Message-ID: <20200729142507.182cd18a@x1.home>
Date:   Wed, 29 Jul 2020 14:25:07 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev()

On Tue, 14 Jul 2020 13:57:02 +0800
Lu Baolu <baolu.lu@...ux.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@...hat.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.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)
>  {