[PATCH v3 2/2] drm/xe: Wait for migration job before unmapping pages

[Thomas Hellström]

On Tue, 2024-12-10 at 17:15 +0100, Nirmoy Das wrote:
> Fix a potential GPU page fault during tt -> system moves by waiting
> for
> migration jobs to complete before unmapping SG. This ensures that
> IOMMU
> mappings are not prematurely torn down while a migration job is still
> in
> progress.
> 
> v2: Use intr=false(Matt A)
> v3: Update commit message(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>
> 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 06931df876ab..0a41b6c0583a 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;
>  }

I assume here we're waiting for the move fence, right? However if
@evict is true, we should hit the ttm_bo_wait_free_node() path. In what
cases do we hit this without evict being true?

Also, shouldn't it be sufficient to wait for DMA_RESV_USAGE_KERNEL
here? 

Thanks,
Thomas