[Intel-gfx] [PATCH 1/2] drm/i915: Document our internal limit on object size

[Chris Wilson]

On Fri, Oct 14, 2016 at 04:18:10PM +0100, Chris Wilson wrote:
> In many places, we try to count pages using a 32 bit integer. That
> implies if we are asked to create an object larger than 43bits, we will
> subtly crash much later. Catch this on the boundary, and add a warning
> to remind ourselves later on our exabyte systems.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  2 +-
>  drivers/gpu/drm/i915/i915_gem.c | 14 ++++++++++++--
>  2 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index fe875b27a6bf..43eb1a72f19e 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3107,7 +3107,7 @@ void i915_gem_object_free(struct drm_i915_gem_object *obj);
>  void i915_gem_object_init(struct drm_i915_gem_object *obj,
>  			 const struct drm_i915_gem_object_ops *ops);
>  struct drm_i915_gem_object *i915_gem_object_create(struct drm_device *dev,
> -						  size_t size);
> +						   u64 size);
>  struct drm_i915_gem_object *i915_gem_object_create_from_data(
>  		struct drm_device *dev, const void *data, size_t size);
>  void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index fe92e28ea0a8..0d1dc04302ec 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4131,14 +4131,24 @@ static const struct drm_i915_gem_object_ops i915_gem_object_ops = {
>  	.put_pages = i915_gem_object_put_pages_gtt,
>  };
>  
> -struct drm_i915_gem_object *i915_gem_object_create(struct drm_device *dev,
> -						  size_t size)
> +struct drm_i915_gem_object *
> +i915_gem_object_create(struct drm_device *dev, u64 size)
>  {
>  	struct drm_i915_gem_object *obj;
>  	struct address_space *mapping;
>  	gfp_t mask;
>  	int ret;
>  
> +	/* There is a prevalence of the assumption that we fit the object's
> +	 * page count inside a 32bit variable. Let's document this and catch
> +	 * if we ever need to fix it.
> +	 */
> +	if (WARN_ON(size >> PAGE_SHIFT > INT_MAX))
> +		return ERR_PTR(-E2BIG);
> +
> +	if (sizeof(size_t) < sizeof(u64) && size > INT_MAX)

What I was looking for here was SIZE_T_MAX. Any ideas?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre