Re: [PATCH v9 11/21] iommufd/device: Move attached device tracking to handle

[Yi Liu <yi.l.liu@intel.com>]

On 2025/3/18 21:56, Jason Gunthorpe wrote:
> On Tue, Mar 18, 2025 at 09:50:12PM +0800, Yi Liu wrote:
>> On 2025/3/18 21:26, Jason Gunthorpe wrote:
>>> On Tue, Mar 18, 2025 at 09:25:56PM +0800, Yi Liu wrote:
>>>>>      	struct iommufd_attach_handle *handle;
>>>>> 	struct xarray device_array;
>>>>> };
>>>>>
>>>>> ?
>>>>>
>>>>> I think I'd just accept the additional allocation and not try to make
>>>>> handle re-usable. Every unique attach gets a unique handle allocation.
>>>>
>>>> If so, we also need to loop the device_array and add the attached devices
>>>> to the new device_array of the new handle.
>>>
>>> Why? Just don't use the handle for that, as above, the handle is still
>>> a pointer that you allocate, and this pasid_enty is another pointer
>>> that is allocated once.
>>
>> I see. How about making a new structure dedicate for tracking attached hwpt
>> and device_array? Like the below. Reusing iommufd_attach_handle structure
>> is not mandatory.
>>
>> struct iommufd_attach {
>>   	struct iommufd_hw_pagetable *hwpt;
>> 	struct xarray device_array;
>> };
> 
> Yeah, something like that would make sense. Then the handle is
> allocated uniquely for every attach.

yes, just keep it as it is today.

> I'd also add info to the kdoc's that handle should not be reused as
> part of the API requirement.

yes. Maybe we can check the stored handle and new handle to fail the same
handle case. I suppose the attach path is fine if reusing handle since
the detach path should fence it.
Regards,
Yi Liu