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drm/i915: Document our internal limit on object size

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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@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161018120251.25043-2-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2016-10-18 13:02:49 +01:00
parent 3ef7f22893
commit b4bcbe2a90
2 changed files with 18 additions and 3 deletions
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2
drivers/gpu/drm/i915/i915_drv.h
View File

@ -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);

19
drivers/gpu/drm/i915/i915_gem.c
View File

@ -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);