Re: [PATCH] drm/i915/gt: handle null ptr at sg traversing

[Matthew Auld <matthew.auld@intel.com>]

On 27/06/2022 18:35, Ramalingam C wrote:
> When calculating the starting address for ccs data in smem scatterlist,
> handle the NULL pointer returned from sg_next, incase of scatterlist
> less than required size..

Do we have some more information on how we can hit this? Is this a 
programmer error? Do we have a testcase?

> 
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_migrate.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_migrate.c b/drivers/gpu/drm/i915/gt/intel_migrate.c
> index 2c35324b5f68..c206fb4f4186 100644
> --- a/drivers/gpu/drm/i915/gt/intel_migrate.c
> +++ b/drivers/gpu/drm/i915/gt/intel_migrate.c
> @@ -669,7 +669,7 @@ calculate_chunk_sz(struct drm_i915_private *i915, bool src_is_lmem,
>   	}
>   }
>   
> -static void get_ccs_sg_sgt(struct sgt_dma *it, u32 bytes_to_cpy)
> +static int get_ccs_sg_sgt(struct sgt_dma *it, u32 bytes_to_cpy)
>   {
>   	u32 len;
>   
> @@ -684,9 +684,13 @@ static void get_ccs_sg_sgt(struct sgt_dma *it, u32 bytes_to_cpy)
>   		bytes_to_cpy -= len;
>   
>   		it->sg = __sg_next(it->sg);
> +		if (!it->sg)
> +			return -EINVAL;
>   		it->dma = sg_dma_address(it->sg);
>   		it->max = it->dma + sg_dma_len(it->sg);
>   	} while (bytes_to_cpy);
> +
> +	return 0;
>   }
>   
>   int
> @@ -745,8 +749,11 @@ intel_context_migrate_copy(struct intel_context *ce,
>   		 * Need to fix it.
>   		 */
>   		ccs_bytes_to_cpy = src_sz != dst_sz ? GET_CCS_BYTES(i915, bytes_to_cpy) : 0;
> -		if (ccs_bytes_to_cpy)
> -			get_ccs_sg_sgt(&it_ccs, bytes_to_cpy);
> +		if (ccs_bytes_to_cpy) {
> +			err = get_ccs_sg_sgt(&it_ccs, bytes_to_cpy);
> +			if (err)
> +				return err;
> +		}
>   	}
>   
>   	src_offset = 0;