Re: [PATCH v4 14/18] drm/i915: object size needs to be u64

[Michel Thierry <michel.thierry@intel.com>]

On 7/7/2015 9:08 PM, Chris Wilson wrote:
> On Tue, Jul 07, 2015 at 04:44:30PM +0100, Michel Thierry wrote:
>> On 7/7/2015 4:27 PM, Chris Wilson wrote:
>>> On Tue, Jul 07, 2015 at 04:14:59PM +0100, Michel Thierry wrote:
>>>> In a 48b world, users can try to allocate buffers bigger than 4GB; in
>>>> these cases it is important that size is a 64b variable.
>>>>
>>>> Also added a warning for illegal bind with size = 0.
>>>>
>>>> Signed-off-by: Michel Thierry <michel.thierry@intel.com>
>>>> ---
>>>>   drivers/gpu/drm/i915/i915_gem.c     | 5 +++--
>>>>   drivers/gpu/drm/i915/i915_gem_gtt.c | 3 +++
>>>>   2 files changed, 6 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>>>> index a0bff41..ebfb789 100644
>>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>>> @@ -3718,7 +3718,8 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
>>>>   {
>>>>   	struct drm_device *dev = obj->base.dev;
>>>>   	struct drm_i915_private *dev_priv = dev->dev_private;
>>>> -	u32 size, fence_size, fence_alignment, unfenced_alignment;
>>>> +	u32 fence_alignment, unfenced_alignment;
>>>> +	u64 size, fence_size;
>>>>   	u64 start =
>>>>   		flags & PIN_OFFSET_BIAS ? flags & PIN_OFFSET_MASK : 0;
>>>>   	u64 end =
>>>> @@ -3777,7 +3778,7 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
>>>>   	 * attempt to find space.
>>>>   	 */
>>>>   	if (size > end) {
>>>> -		DRM_DEBUG("Attempting to bind an object (view type=%u) larger than the aperture: size=%u > %s aperture=%llu\n",
>>>> +		DRM_DEBUG("Attempting to bind an object (view type=%u) larger than the aperture: size=%llu > %s aperture=%llu\n",
>>>>   			  ggtt_view ? ggtt_view->type : 0,
>>>>   			  size,
>>>>   			  flags & PIN_MAPPABLE ? "mappable" : "total",
>>>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>> index 449a245..900bce6 100644
>>>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>>>> @@ -3312,6 +3312,9 @@ int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,
>>>>   	if (WARN_ON(flags == 0))
>>>>   		return -EINVAL;
>>>>
>>>> +	if (WARN_ON(vma->node.size == 0))
>>>> +		return -EINVAL;
>>>
>>> This is superfluous. We don't allow size=0 object creation, and the test
>>> is better (if at all) at vma_create, but what you mean here is
>>> WARN_ON(!drm_mm_node_allocated()) which seems sensisble. And both of
>>> these would be better as ENODEV so we don't confuse the user when they
>>> get propagated back to userspace.
>>> -Chris
>>>
>> My idea was to catch the node.size overflow if the variable is
>> inadvertently changed back to u32 (which has already happen in other
>> places).
>
> Ok, that didn't come across when I just read node.size == 0 (what are
> chances that node.size was exactly 2^32 and then truncated?)
>
Only a test explicitly looking for this kind of issues (I guess). In 
that test, objects bigger than 2^32 were truncated, while objects 
exactly 2^32 were hitting a WARN in the driver; alloc_pages wouldn't do 
anything because node.size == 0, and then insert would complain no pages 
existed.

> vma->node should be fairly opaque, and if possible we want the checks in
> drm_mm.c - if we can think of good tests for that layer.
>
> Certainly drm_mm_reserve_node() probably wants a few sanity checks.
> Though most of those should fall out when it can't do the reservation
> the user requests.
Or change drm_mm_insert_node_in_range_generic() to warn when size==0?


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