Re: [PATCH v2 4/5] iommu: Support mm PASID 1:n with sva domains

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2023/8/27 16:44, 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()).
> 
> 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.
> 
> Signed-off-by: Tina Zhang <tina.zhang@intel.com>
> ---
>   drivers/iommu/iommu-sva.c | 38 +++++++++++++++++++++++++-------------
>   include/linux/iommu.h     | 10 +++-------
>   kernel/fork.c             |  1 -
>   3 files changed, 28 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 0a4a1ed40814c..35366f51ad27d 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 = NULL;

No need to initialize this variable.

>   	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;
> +	mm->iommu_mm = iommu_mm;
> +	INIT_LIST_HEAD(&mm->iommu_mm->sva_domains);

If you change the order of the two lines above, it will look more
comfortable.

>   
> -	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 937f3abc26f2e..cfbd35ceb375f 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -109,6 +109,7 @@ struct iommu_domain {
>   		struct {	/* IOMMU_DOMAIN_SVA */
>   			struct mm_struct *mm;
>   			int users;
> +			struct list_head next;

It looks better if you add a comment to describe how this list node is
used and how the list is protected.

>   		};
>   	};
>   };
> @@ -1177,17 +1178,13 @@ 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 +1210,6 @@ 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 d2e12b6d2b180..f06392dd1ca8a 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);

This patch overall looks good to me. With above nits addressed,

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu