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

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Date:   Fri, 22 Sep 2023 09:07:28 +0800
From:   Tina Zhang <tina.zhang@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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

Hi Jason,

On 9/22/23 07:31, Jason Gunthorpe wrote:
> 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)
Good suggestion. Thanks.

> 
> (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.
Right. Thanks.


Regards,
-Tina
> 
> Otherwise the logic looks OK.
> 
> Jason
>