linux-kernel - Re: [PATCH v4 5/6] iommu: Support mm PASID 1:n with sva domains

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Message-ID: <20230921233133.GB13795@ziepe.ca>
Date:   Thu, 21 Sep 2023 20:31:33 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Michael Shavit <mshavit@...gle.com>,
        Vasant Hegde <vasant.hegde@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/6] iommu: Support mm PASID 1:n with sva domains

On Tue, Sep 12, 2023 at 08:59:35PM +0800, Tina Zhang wrote:
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 0f956ecd0c9b..79779bbef653 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -15,6 +15,7 @@ static DEFINE_MUTEX(iommu_sva_lock);
>  static int iommu_sva_alloc_pasid(struct mm_struct *mm, struct device *dev)
>  {
>  	ioasid_t pasid;
> +	struct iommu_mm_data *iommu_mm;
>  	int ret = 0;
>  
>  	if (!arch_pgtable_dma_compat(mm))
> @@ -28,12 +29,22 @@ static int iommu_sva_alloc_pasid(struct mm_struct *mm, struct device *dev)
>  		goto out;
>  	}
>  
> +	iommu_mm = kzalloc(sizeof(struct iommu_mm_data), GFP_KERNEL);
> +	if (!iommu_mm) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
>  	pasid = iommu_alloc_global_pasid(dev);
>  	if (pasid == IOMMU_PASID_INVALID) {
> +		kfree(iommu_mm);
>  		ret = -ENOSPC;
>  		goto out;
>  	}
> -	mm->pasid = pasid;
> +	iommu_mm->pasid = pasid;
> +	INIT_LIST_HEAD(&iommu_mm->sva_domains);
> +	mm->iommu_mm = iommu_mm;
> +
>  	ret = 0;
>  out:
>  	mutex_unlock(&iommu_sva_lock);
> @@ -73,16 +84,12 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>  
>  	mutex_lock(&iommu_sva_lock);
>  	/* Search for an existing domain. */
> -	domain = iommu_get_domain_for_dev_pasid(dev, mm_get_pasid(mm),
> -						IOMMU_DOMAIN_SVA);
> -	if (IS_ERR(domain)) {
> -		ret = PTR_ERR(domain);
> -		goto out_unlock;
> -	}
> -
> -	if (domain) {
> -		domain->users++;
> -		goto out;
> +	list_for_each_entry(domain, &mm->iommu_mm->sva_domains, next) {
> +		ret = iommu_attach_device_pasid(domain, dev, mm_get_pasid(mm));
> +		if (!ret) {
> +			domain->users++;
> +			goto out;
> +		}
>  	}
>  
>  	/* Allocate a new domain and set it on device pasid. */
> @@ -96,6 +103,8 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm
>  	if (ret)
>  		goto out_free_domain;
>  	domain->users = 1;
> +	list_add(&domain->next, &mm->iommu_mm->sva_domains);
> +
>  out:
>  	mutex_unlock(&iommu_sva_lock);
>  	handle->dev = dev;
> @@ -128,8 +137,9 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
>  	struct device *dev = handle->dev;
>  
>  	mutex_lock(&iommu_sva_lock);
> +	iommu_detach_device_pasid(domain, dev, pasid);
>  	if (--domain->users == 0) {
> -		iommu_detach_device_pasid(domain, dev, pasid);
> +		list_del(&domain->next);
>  		iommu_domain_free(domain);
>  	}
>  	mutex_unlock(&iommu_sva_lock);
> @@ -209,4 +219,5 @@ void mm_pasid_drop(struct mm_struct *mm)
>  		return;
>  
>  	iommu_free_global_pasid(mm_get_pasid(mm));
> +	kfree(mm->iommu_mm);
>  }
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index b9c9f14a95cc..c61bc45d5a82 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -109,6 +109,11 @@ struct iommu_domain {
>  		struct {	/* IOMMU_DOMAIN_SVA */
>  			struct mm_struct *mm;
>  			int users;
> +			/*
> +			 * Next iommu_domain in mm->iommu_mm->sva-domains list
> +			 * protected by iommu_sva_lock.
> +			 */
> +			struct list_head next;
>  		};
>  	};
>  };
> @@ -1186,17 +1191,13 @@ 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;
> -}
>  static inline bool mm_valid_pasid(struct mm_struct *mm)
>  {
> -	return mm->pasid != IOMMU_PASID_INVALID;
> +	return mm->iommu_mm ? true : false;
>  }

HUm this isn't locked very nicely.

Above do

smp_store_release(&mm->iommu_mm, iommu_mm);

And then do 

  return READ_ONCE(mm->iommu_mm)

(no need for ternaries with bools, compiler generates it automatically)


>  static inline u32 mm_get_pasid(struct mm_struct *mm)
>  {
> -	return mm->pasid;
> +	return mm->iommu_mm ? mm->iommu_mm->pasid : IOMMU_PASID_INVALID;
>  }

Then this should be

struct iommu_mm_data *iommu_mm = READ_ONCE(mm->iommu_mm);

if (!iommu_mm)
   return IOMMU_PASID_INVALID;
return iommu_mm->pasid;

Keeping in mind that the kfree(mm->iommu_mm) being placed in the
mm_drop is critical to this working safely.

Otherwise the logic looks OK.

Jason