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

[Matthew Auld]

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?

Maybe add some more info to the commit message? 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>

> ---
>   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;
>   }