Re: [PATCH v12 05/17] iommu: Add attach/detach_dev_pasid iommu interface

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

On 2022/8/26 22:37, Jason Gunthorpe wrote:
> On Fri, Aug 26, 2022 at 08:11:29PM +0800, Lu Baolu wrote:
> 
>> + * iommu_get_domain_for_dev_pasid() - Retrieve domain for @pasid of @dev
>> + * @dev: the queried device
>> + * @pasid: the pasid of the device
>> + * @type: matched domain type, 0 for any match
>> + *
>> + * This is a variant of iommu_get_domain_for_dev(). It returns the existing
>> + * domain attached to pasid of a device. It's only for internal use of the
>> + * IOMMU subsystem.
> 
> If it is only for external use then why is it exported?
> 
> I would add something like:
> 
>   Callers must hold a lock around this function, and both
>   iommu_attach/detach_dev_pasid() whenever a domain of type is being
>   manipulated. This API does not internally resolve races with
>   attach/detach.

Yes. Updated. This is what this API expected.

> 
>> + * detaching from the device PASID.
>> + *
>> + * Return: attached domain on success, NULL otherwise.
>> + */
>> +struct iommu_domain *iommu_get_domain_for_dev_pasid(struct device *dev,
>> +						    ioasid_t pasid,
>> +						    unsigned int type)
>> +{
>> +	struct iommu_domain *domain;
>> +	struct iommu_group *group;
>> +
>> +	group = iommu_group_get(dev);
>> +	if (!group)
>> +		return NULL;
>> +	/*
>> +	 * The xarray protects its internal state with RCU. Hence the domain
>> +	 * obtained is either NULL or fully formed.
>> +	 */
> 
> This has nothing to do with RCU
> 
> xa_lock() is used to ensure that the domain pointer remains valid
> while we check the type since it blocks concurrent xa_erase().

With xa_lock() added, this comment is not needed anymore.

Best regards,
baolu