[RFC PATCH 3/3] pseries/iommu: Enable DDW for VFIO TCE create

[Shivaprasad G Bhat]

Hi Michael,

On 3/13/24 18:23, Michael Ellerman wrote:
> Hi Shivaprasad,
>
> Shivaprasad G Bhat <sbhat at linux.ibm.com> writes:
>> The commit 9d67c9433509 ("powerpc/iommu: Add \"borrowing\"
>> iommu_table_group_ops") implemented the "borrow" mechanism for
>> the pSeries SPAPR TCE. It did implement this support partially
>> that it left out creating the DDW if not present already.
>>
>> The patch here attempts to fix the missing gaps.
>>   - Expose the DDW info to user by collecting it during probe.
>>   - Create the window and the iommu table if not present during
>>     VFIO_SPAPR_TCE_CREATE.
>>   - Remove and recreate the window if the pageshift and window sizes
>>     do not match.
>>   - Restore the original window in enable_ddw() if the user had
>>     created/modified the DDW. As there is preference for DIRECT mapping
>>     on the host driver side, the user created window is removed.
>>
>> The changes work only for the non-SRIOV-VF scenarios for PEs having
>> 2 DMA windows.
> This crashes on powernv.


Thanks for pointing this out.  I will take care of this in v2 of this RFC.


Regards,

Shivaprasad