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Commit b4bcbe2a authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Document our internal limit on object size 



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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161018120251.25043-2-chris@chris-wilson.co.uk
parent 3ef7f228

drivers/gpu/drm/i915/i915_drv.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

drivers/gpu/drm/i915/i915_gem.c

+17 −2
Original line number Diff line number Diff line
@@ -4131,14 +4131,29 @@ 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)

/* Note we don't consider signbits :| */

#define overflows_type(x, T) \

	(sizeof(x) > sizeof(T) && (x) >> (sizeof(T) * BITS_PER_BYTE))



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 _signed_ variable. Let's document this and

	 * catch if we ever need to fix it. In the meantime, if you do spot

	 * such a local variable, please consider fixing!

	 */

	if (WARN_ON(size >> PAGE_SHIFT > INT_MAX))

		return ERR_PTR(-E2BIG);



	if (overflows_type(size, obj->base.size))

		return ERR_PTR(-E2BIG);



	obj = i915_gem_object_alloc(dev);

	if (obj == NULL)

		return ERR_PTR(-ENOMEM);