[PATCH v2 2/2] drm/xe: Wait for migration job before unmapping pages

[Nirmoy Das]

On 12/5/2024 1:40 PM, Matthew Auld wrote:
> On 05/12/2024 12:02, Nirmoy Das wrote:
>> There could be still migration job going on while doing
>> xe_tt_unmap_sg() which could trigger GPU page faults. Fix this by
>> waiting for the migration job to finish.
>>
>> v2: Use intr=false(Matt A)
>>
>> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3466
>> Fixes: 75521e8b56e8 ("drm/xe: Perform dma_map when moving system buffer objects to TT")
>> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: Lucas De Marchi <lucas.demarchi at intel.com>
>> Cc: <stable at vger.kernel.org> # v6.11+
>> Cc: Matthew Auld <matthew.auld at intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
>
> Ok, so this is something like ttm_bo_move_to_ghost() doing a pipeline move for tt -> system, but we then do xe_tt_unmap_sg() too early which tears down the IOMMU (if enabled) mappings whilst the job is in progress?
Yes, this exactly what is happening for this issue.
>
> Maybe add some more info to the commit message? 

I will add more details.


> I think this for sure fixes it. Just wondering if it's somehow possible to keep the mapping until the job is done, since all tt -> sys moves are now synced here?
>
> Unless Thomas has a better idea here,
> Reviewed-by: Matthew Auld <matthew.auld at intel.com>


Thanks,

Nirmoy

>
>> ---
>>   drivers/gpu/drm/xe/xe_bo.c | 10 +++++++++-
>>   1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index b2aa368a23f8..c906a5529db0 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -857,8 +857,16 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
>>     out:
>>       if ((!ttm_bo->resource || ttm_bo->resource->mem_type == XE_PL_SYSTEM) &&
>> -        ttm_bo->ttm)
>> +        ttm_bo->ttm) {
>> +        long timeout = dma_resv_wait_timeout(ttm_bo->base.resv,
>> +                             DMA_RESV_USAGE_BOOKKEEP,
>> +                             false,
>> +                             MAX_SCHEDULE_TIMEOUT);
>> +        if (timeout < 0)
>> +            ret = timeout;
>> +
>>           xe_tt_unmap_sg(ttm_bo->ttm);
>> +    }
>>         return ret;
>>   }
>