Re: [PATCH v2 11/12] iommu/vt-d: Use device_domain_lock accurately

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

On 2022/6/14 15:16, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Tuesday, June 14, 2022 10:52 AM
>>
>> The device_domain_lock is used to protect the device tracking list of
>> a domain. Remove unnecessary spin_lock/unlock()'s and move the necessary
>> ones around the list access.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 68 +++++++++++++++----------------------
>>   1 file changed, 27 insertions(+), 41 deletions(-)
>>
> [...]
>> +iommu_support_dev_iotlb(struct dmar_domain *domain, struct
>> intel_iommu *iommu,
>> +			u8 bus, u8 devfn)
>>   {
>> -	struct device_domain_info *info;
>> -
>> -	assert_spin_locked(&device_domain_lock);
>> +	struct device_domain_info *info = NULL, *tmp;
>> +	unsigned long flags;
>>
>>   	if (!iommu->qi)
>>   		return NULL;
>>
>> -	list_for_each_entry(info, &domain->devices, link)
>> -		if (info->iommu == iommu && info->bus == bus &&
>> -		    info->devfn == devfn) {
>> -			if (info->ats_supported && info->dev)
>> -				return info;
>> +	spin_lock_irqsave(&device_domain_lock, flags);
>> +	list_for_each_entry(tmp, &domain->devices, link) {
>> +		if (tmp->iommu == iommu && tmp->bus == bus &&
>> +		    tmp->devfn == devfn) {
>> +			if (tmp->ats_supported)
>> +				info = tmp;
> 
> Directly returning with unlock here is clearer than adding
> another tmp variable...

Sure.

> 
>> @@ -2460,15 +2450,14 @@ static int domain_add_dev_info(struct
>> dmar_domain *domain, struct device *dev)
>>   	if (!iommu)
>>   		return -ENODEV;
>>
>> -	spin_lock_irqsave(&device_domain_lock, flags);
>> -	info->domain = domain;
>>   	ret = domain_attach_iommu(domain, iommu);
>> -	if (ret) {
>> -		spin_unlock_irqrestore(&device_domain_lock, flags);
>> +	if (ret)
>>   		return ret;
>> -	}
>> +
>> +	spin_lock_irqsave(&device_domain_lock, flags);
>>   	list_add(&info->link, &domain->devices);
>>   	spin_unlock_irqrestore(&device_domain_lock, flags);
>> +	info->domain = domain;
>>
> 
> This is incorrect. You need fully initialize the object before adding
> it to the list. Otherwise a search right after above unlock and
> before assigning info->domain will get a wrong data

Fair enough. Will fix it in the next version.

Best regards,
baolu