linux-kernel - Re: [PATCH RFC 09/11] iommu: Add iommu_get_domain_for_dev

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Date:   Tue, 22 Mar 2022 12:50:45 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 09/11] iommu: Add iommu_get_domain_for_dev_pasid()

On 2022/3/21 20:40, Jason Gunthorpe wrote:
> On Sun, Mar 20, 2022 at 02:40:28PM +0800, Lu Baolu wrote:
>> @@ -3098,7 +3101,16 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
>>   	if (iommu_group_device_count(group) != 1)
>>   		goto out_unlock;
>>   
>> +	xa_lock(&group->pasid_array);
>> +	curr = __xa_cmpxchg(&group->pasid_array, pasid, NULL,
>> +			    domain, GFP_KERNEL);
>> +	xa_unlock(&group->pasid_array);
>> +	if (curr)
> 
> curr can be an xa_err that should be propogated.

Yes, should check xa_err().

> 
>> +		goto out_unlock;
>> +
>>   	ret = domain->ops->attach_dev_pasid(domain, dev, pasid);
>> +	if (ret)
>> +		xa_erase(&group->pasid_array, pasid);
>>   
>>   out_unlock:
>>   	mutex_unlock(&group->mutex);
>> @@ -3118,6 +3130,25 @@ void iommu_detach_device_pasid(struct iommu_domain *domain,
>>   
>>   	mutex_lock(&group->mutex);
>>   	domain->ops->detach_dev_pasid(domain, dev, pasid);
>> +	xa_erase(&group->pasid_array, pasid);
>> +	mutex_unlock(&group->mutex);
>> +	iommu_group_put(group);
>> +}
>> +
>> +struct iommu_domain *
>> +iommu_get_domain_for_dev_pasid(struct device *dev, ioasid_t pasid)
>> +{
>> +	struct iommu_domain *domain;
>> +	struct iommu_group *group;
>> +
>> +	group = iommu_group_get(dev);
>> +	if (!group)
>> +		return NULL;
>> +
>> +	mutex_lock(&group->mutex);
>> +	domain = xa_load(&group->pasid_array, pasid);
>>   	mutex_unlock(&group->mutex);
>>   	iommu_group_put(group);
> 
> This whole API seems sketchy - what is the lifecycle of the returned
> iommu_domain and what prevents it from being concurrently freed after
> unlocking?

Agreed. The domain could be used in page fault handling thread, hence
need a mechanism to guarantee the concurrence.

Best regards,
baolu