Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA interfaces

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

On 2022/5/12 13:44, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@linux.intel.com>
>> Sent: Thursday, May 12, 2022 1:17 PM
>>
>> On 2022/5/12 13:01, Tian, Kevin wrote:
>>>> From: Baolu Lu <baolu.lu@linux.intel.com>
>>>> Sent: Thursday, May 12, 2022 11:03 AM
>>>>
>>>> On 2022/5/11 22:53, Jason Gunthorpe wrote:
>>>>>>> Also, given the current arrangement it might make sense to have a
>>>>>>> struct iommu_domain_sva given that no driver is wrappering this in
>>>>>>> something else.
>>>>>> Fair enough. How about below wrapper?
>>>>>>
>>>>>> +struct iommu_sva_domain {
>>>>>> +       /*
>>>>>> +        * Common iommu domain header,*must*  be put at the top
>>>>>> +        * of the structure.
>>>>>> +        */
>>>>>> +       struct iommu_domain domain;
>>>>>> +       struct mm_struct *mm;
>>>>>> +       struct iommu_sva bond;
>>>>>> +}
>>>>>>
>>>>>> The refcount is wrapped in bond.
>>>>> I'm still not sure that bond is necessary
>>>>
>>>> "bond" is the sva handle that the device drivers get through calling
>>>> iommu_sva_bind().
>>>>
>>>
>>> 'bond' was required before because we didn't have a domain to wrap
>>> the page table at that time.
>>>
>>> Now we have a domain and it is 1:1 associated to bond. Probably
>>> make sense now by just returning the domain as the sva handle
>>> instead?
>>
>> It also includes the device information that the domain has been
>> attached. So the sva_unbind() looks like this:
>>
>> /**
>>    * iommu_sva_unbind_device() - Remove a bond created with
>> iommu_sva_bind_device
>>    * @handle: the handle returned by iommu_sva_bind_device()
>>    *
>>    * Put reference to a bond between device and address space. The device
>> should
>>    * not be issuing any more transaction for this PASID. All outstanding page
>>    * requests for this PASID must have been flushed to the IOMMU.
>>    */
>> void iommu_sva_unbind_device(struct iommu_sva *handle)
>>
>> It's fine to replace the iommu_sva with iommu_sva_domain for sva handle,
>> if we can include the device in the unbind() interface.
> 
> can we just have unbind(domain, device)?

Yes. With this, we can remove bond.

This could be done in below phase 2.

> 
>>
>> Anyway, I'd expect to achieve all these in two steps:
>>
>> - sva and iopf refactoring, only iommu internal changes;
>> - sva interface refactoring, only interface changes.
>>
>> Does above work?
>>
>> Best regards,
>> baolu

Best regards,
baolu