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

[Tvrtko Ursulin]

On 14/10/2016 16:24, Chris Wilson wrote:
> 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?

Would (1ULL << (sizeof(size_t) * BITS_PER_BYTE)) - 1 work?

Regards,

Tvrtko