Re: [Intel-gfx] [PATCH] drm/i915/ttm: Fix access_memory null pointer exception

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 13.10.2022 19:56, Jonathan Cavitt wrote:
> i915_ttm_to_gem can return a NULL pointer, which is
> dereferenced in i915_ttm_access_memory without first
> checking if it is NULL.  Inspecting
> i915_ttm_io_mem_reserve, it appears the correct
> behavior in this case is to return -EINVAL.
> 
> Fixes: 26b15eb0 ("drm/i915/ttm: implement access_memory")
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> Suggested-by: John C Harrison <John.C.Harrison@intel.com>
> CC: Matthew Auld <matthew.auld@intel.com>
> CC: Andrzej Hajda <andrzej.hajda@intel.com>
> CC: Nirmoy Das <nirmoy.das@intel.com>
> CC: Andi Shyti <andi.shyti@linux.intel.com> > ---
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index d63f30efd631..b569624f2ed9 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -704,11 +704,16 @@ static int i915_ttm_access_memory(struct ttm_buffer_object *bo,
>   				  int len, int write)
>   {
>   	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
> -	resource_size_t iomap = obj->mm.region->iomap.base -
> -		obj->mm.region->region.start;
> +	resource_size_t iomap;
>   	unsigned long page = offset >> PAGE_SHIFT;
>   	unsigned long bytes_left = len;
>   
> +	if (!obj)
> +		return -EINVAL;
> +
> +	iomap = obj->mm.region->iomap.base -
> +		obj->mm.region->region.start;
> +

There are 4 occurrences of this subtraction in the code, enough for 
helper :) ?

Anyway:
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>

Regards
Andrzej

>   	/*
>   	 * TODO: For now just let it fail if the resource is non-mappable,
>   	 * otherwise we need to perform the memcpy from the gpu here, without