linux-kernel - Re: [PATCH v10 08/12] iommu/sva: Refactoring iommu_sva_bind/unbind

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Date:   Sat, 23 Jul 2022 11:26:50 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 08/12] iommu/sva: Refactoring
 iommu_sva_bind/unbind_device()

On Tue, Jul 05, 2022 at 01:07:06PM +0800, Lu Baolu wrote:
> The existing iommu SVA interfaces are implemented by calling the SVA
> specific iommu ops provided by the IOMMU drivers. There's no need for
> any SVA specific ops in iommu_ops vector anymore as we can achieve
> this through the generic attach/detach_dev_pasid domain ops.
> 
> This refactors the IOMMU SVA interfaces implementation by using the
> set/block_pasid_dev ops and align them with the concept of the SVA
> iommu domain. Put the new SVA code in the sva related file in order
> to make it self-contained.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Tested-by: Zhangfei Gao <zhangfei.gao@...aro.org>
> Tested-by: Tony Zhu <tony.zhu@...el.com>
> ---
>  include/linux/iommu.h         |  67 +++++++++++--------
>  drivers/iommu/iommu-sva-lib.c |  98 ++++++++++++++++++++++++++++
>  drivers/iommu/iommu.c         | 119 ++++++++--------------------------
>  3 files changed, 165 insertions(+), 119 deletions(-)
> 
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 42f0418dc22c..f59b0ecd3995 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -39,7 +39,6 @@ struct device;
>  struct iommu_domain;
>  struct iommu_domain_ops;
>  struct notifier_block;
> -struct iommu_sva;
>  struct iommu_fault_event;
>  struct iommu_dma_cookie;
>  
> @@ -57,6 +56,14 @@ struct iommu_domain_geometry {
>  	bool force_aperture;       /* DMA only allowed in mappable range? */
>  };
>  
> +/**
> + * struct iommu_sva - handle to a device-mm bond
> + */
> +struct iommu_sva {
> +	struct device		*dev;
> +	refcount_t		users;
> +};
> +
>  /* Domain feature flags */
>  #define __IOMMU_DOMAIN_PAGING	(1U << 0)  /* Support for iommu_map/unmap */
>  #define __IOMMU_DOMAIN_DMA_API	(1U << 1)  /* Domain for use in DMA-API
> @@ -105,6 +112,7 @@ struct iommu_domain {
>  		};
>  		struct {	/* IOMMU_DOMAIN_SVA */
>  			struct mm_struct *mm;
> +			struct iommu_sva bond;

We can't store a single struct device inside a domain, this is not
layed out right.

The API is really refcounting the PASID:

> +struct iommu_sva *iommu_sva_bind_device(struct device *dev,
> +					struct mm_struct *mm);
> +void iommu_sva_unbind_device(struct iommu_sva *handle);

So what you need to do is store that 'iommu_sva' in the group's PASID
xarray.

The bind logic would be

  sva = xa_load(group->pasid, mm->pasid)
  if (sva)
     refcount_inc(sva->users)
     return sva
  sva = kalloc
  sva->domain = domain
  xa_store(group->pasid, sva);

Jason