linux-kernel - Re: [RFC PATCH 5/6] iommu: Support mm PASID 1:1 with sva domain

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Date:   Mon, 10 Jul 2023 14:28:37 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Michael Shavit <mshavit@...gle.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/6] iommu: Support mm PASID 1:1 with sva domain

On Fri, Jul 07, 2023 at 09:34:40AM +0800, Tina Zhang wrote:
> Each mm bound to devices gets a PASID and a corresponding sva domain
> allocated in iommu_sva_bind_device(), which are referenced by iommu_mm
> field of the mm. And that PASID and sva domain get released in iommu_sva_
> unbind_device() when no devices are binding to that mm. As a result,
> during the life cycle, sva domain has 1:1 with mm PASID.
> 
> Since the required info of PASID and sva domain are kept in struct
> iommu_mm_data of a mm, use mm->iommu_mm field instead of the old pasid
> field in mm struct.

This is not technically right, the domains need to be a list, and we
need to search the list. Almost always the list will have 0 or 1
entries in it.

> @@ -88,31 +98,41 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>  		goto out_unlock;
>  	}
>  
> -	if (domain) {
> -		domain->users++;
> -		goto out;
> +	if (unlikely(domain)) {
> +		/* Re-attach the device to the same domain? */
> +		if (domain == sva_domain) {
> +			goto out;
> +		} else {
> +			/* Didn't get detached from the previous domain? */
> +			ret = -EBUSY;
> +			goto out_unlock;
> +		}
>  	}

And if we do all of this we should just get rid of the horrible
iommu_get_domain_for_dev_pasid() entirely.

> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 20135912584ba..1511ded7bc910 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -1175,20 +1175,20 @@ static inline bool tegra_dev_iommu_get_stream_id(struct device *dev, u32 *stream
>  #ifdef CONFIG_IOMMU_SVA
>  static inline void mm_pasid_init(struct mm_struct *mm)
>  {
> -	mm->pasid = IOMMU_PASID_INVALID;
> +	mm->iommu_mm = &default_iommu_mm;
>  }
>  static inline bool mm_valid_pasid(struct mm_struct *mm)
>  {
> -	return mm->pasid != IOMMU_PASID_INVALID;
> +	return mm->iommu_mm->pasid != IOMMU_PASID_INVALID;
>  }

And these can now just test if the iommu_mmu->sva_domain is NULL

Jaon