Re: [PATCH v3 5/6] iommu: Support mm PASID 1:n with sva domains

[Vasant Hegde <vasant.hegde@amd.com>]

On 9/5/2023 5:39 AM, Tina Zhang wrote:
> Each mm bound to devices gets a PASID and corresponding sva domains
> allocated in iommu_sva_bind_device(), which are referenced by iommu_mm
> field of the mm. The PASID is released in __mmdrop(), while a sva domain
> is released when no one is using it (the reference count is decremented
> in iommu_sva_unbind_device()). However, although sva domains and their
> PASID are separate objects such that their own life cycles could be
> handled independently, an enqcmd use case may require releasing the
> PASID in releasing the mm (i.e., once a PASID is allocated for a mm, it
> will be permanently used by the mm and won't be released until the end
> of mm) and only allows to drop the PASID after the sva domains are
> released. To this end, mmgrab() is called in iommu_sva_domain_alloc() to
> increment the mm reference count and mmdrop() is invoked in
> iommu_domain_free() to decrement the mm reference count.
> 
> Since the required info of PASID and sva domains is kept in struct
> iommu_mm_data of a mm, use mm->iommu_mm field instead of the old pasid
> field in mm struct. The sva domain list is protected by iommu_sva_lock.
> 
> Besides, this patch removes mm_pasid_init(), as with the introduced
> iommu_mm structure, initializing mm pasid in mm_init() is unnecessary.
> 
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Tina Zhang <tina.zhang@intel.com>

Looks good to me.

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant

> ---
> 
> Changes in v3:
> - Add a comment describing domain->next.
> - Update the commit message.
> 
>  drivers/iommu/iommu-sva.c | 38 +++++++++++++++++++++++++-------------
>  include/linux/iommu.h     | 14 +++++++-------
>  kernel/fork.c             |  1 -
>  3 files changed, 32 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 0a4a1ed40814..e7e3aeaa7055 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -15,6 +15,7 @@ static DEFINE_IDA(iommu_global_pasid_ida);
>  /* Allocate a PASID for the mm within range (inclusive) */
>  static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
>  {
> +	struct iommu_mm_data *iommu_mm;
>  	int ret = 0;
>  
>  	if (min == IOMMU_PASID_INVALID ||
> @@ -33,11 +34,22 @@ static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t ma
>  		goto out;
>  	}
>  
> +	iommu_mm = kzalloc(sizeof(struct iommu_mm_data), GFP_KERNEL);
> +	if (!iommu_mm) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
>  	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_KERNEL);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		kfree(iommu_mm);
>  		goto out;
> +	}
> +
> +	iommu_mm->pasid = ret;
> +	INIT_LIST_HEAD(&iommu_mm->sva_domains);
> +	mm->iommu_mm = iommu_mm;
>  
> -	mm->pasid = ret;
>  	ret = 0;
>  out:
>  	mutex_unlock(&iommu_sva_lock);
> @@ -82,16 +94,12 @@ 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. */
> @@ -105,6 +113,8 @@ 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;
> @@ -137,8 +147,9 @@ 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);
> @@ -218,4 +229,5 @@ void mm_pasid_drop(struct mm_struct *mm)
>  		return;
>  
>  	ida_free(&iommu_global_pasid_ida, mm_get_pasid(mm));
> +	kfree(mm->iommu_mm);
>  }
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 937f3abc26f2..95ada53f24ec 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;
>  		};
>  	};
>  };
> @@ -1177,17 +1182,13 @@ 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;
>  }
>  static inline u32 mm_get_pasid(struct mm_struct *mm)
>  {
> -	return mm->pasid;
> +	return mm->iommu_mm ? mm->iommu_mm->pasid : IOMMU_PASID_INVALID;
>  }
>  static inline u32 mm_get_enqcmd_pasid(struct mm_struct *mm)
>  {
> @@ -1213,7 +1214,6 @@ static inline u32 iommu_sva_get_pasid(struct iommu_sva *handle)
>  {
>  	return IOMMU_PASID_INVALID;
>  }
> -static inline void mm_pasid_init(struct mm_struct *mm) {}
>  static inline bool mm_valid_pasid(struct mm_struct *mm) { return false; }
>  static inline u32 mm_get_pasid(struct mm_struct *mm)
>  {
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d2e12b6d2b18..f06392dd1ca8 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1274,7 +1274,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
>  	mm_init_cpumask(mm);
>  	mm_init_aio(mm);
>  	mm_init_owner(mm, p);
> -	mm_pasid_init(mm);
>  	RCU_INIT_POINTER(mm->exe_file, NULL);
>  	mmu_notifier_subscriptions_init(mm);
>  	init_tlb_flush_pending(mm);