[PATCH v2] drm/gem: fix mmap vma size calculations

[David Herrmann]

Hi

On Tue, Jul 30, 2013 at 9:52 AM, Sedat Dilek <sedat.dilek at gmail.com> wrote:
> On Tue, Jul 30, 2013 at 9:41 AM, Sedat Dilek <sedat.dilek at gmail.com> wrote:
>> On Fri, Jul 26, 2013 at 10:15 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>> On Fri, Jul 26, 2013 at 12:09:32PM +0200, David Herrmann wrote:
>>>> The VMA manager is page-size based so drm_vma_node_size() returns the size
>>>> in pages. However, drm_gem_mmap_obj() requires the size in bytes. Apply
>>>> PAGE_SHIFT so we no longer get EINVAL during mmaps due to too small
>>>> buffers.
>>>>
>>>> This bug was introduced in commit:
>>>>   0de23977cfeb5b357ec884ba15417ae118ff9e9b
>>>>   "drm/gem: convert to new unified vma manager"
>>>>
>>>> Fixes i915 gtt mmap failure reported by Sedat Dilek in:
>>>>   Re: linux-next: Tree for Jul 25 [ call-trace: drm | drm-intel related? ]
>>>>
>>>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>>>> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
>>>> Reported-by: Sedat Dilek <sedat.dilek at gmail.com>
>>>> Tested-by: Sedat Dilek <sedat.dilek at gmail.com>
>>>
>>> I remember that I even checked whether v4 was consistent with pages vs.
>>> bytes ;-) So
>>>
>>
>> Hi David, Daniel, and Dave,
>>
>> Just reading quickly "drm: add unified vma offset manager"... is that
>> below in the docs?
>>
>> "The VMA manager is page-size based so drm_vma_node_size() returns the size
>> in pages. However, drm_gem_mmap_obj() requires the size in bytes. Apply
>> PAGE_SHIFT so we no longer get EINVAL during mmaps due to too small
>> buffers."
>>
>> If not, do you mind adding it?
>>
>
> To quote this two:
>
> [ include/drm/drm_vma_manager.h ]
>
> /**
>  * drm_vma_node_size() - Return size (page-based)
>  * @node: Node to inspect
>  *
>  * Return the size as number of pages for the given node. This is the same size
>  * that was passed to drm_vma_offset_add(). If no offset is allocated for the
>  * node, this is 0.
>  *
>  * RETURNS:
>  * Size of @node as number of pages. 0 if the node does not have an offset
>  * allocated.
>  */
>
> [ drivers/gpu/drm/drm_gem.c ]

It's actually "drm_gem_mmap_obj" which we have to look at and it says:
  * @obj_size: the object size to be mapped, in bytes

So both are already documented.

Regards
David

> /**
>  * drm_gem_mmap - memory map routine for GEM objects
>  * @filp: DRM file pointer
>  * @vma: VMA for the area to be mapped
>  *
>  * If a driver supports GEM object mapping, mmap calls on the DRM file
>  * descriptor will end up here.
>  *
>  * Look up the GEM object based on the offset passed in (vma->vm_pgoff will
>  * contain the fake offset we created when the GTT map ioctl was called on
>  * the object) and map it with a call to drm_gem_mmap_obj().
>  */
>
> - Sedat -
>
>> Thanks in advance!
>>
>> - Sedat -
>>
>>> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>
>>> on this little fixup.
>>> -Daniel
>>>
>>>> ---
>>>>  drivers/gpu/drm/drm_gem.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>>> index 3613b50..1f76572 100644
>>>> --- a/drivers/gpu/drm/drm_gem.c
>>>> +++ b/drivers/gpu/drm/drm_gem.c
>>>> @@ -666,7 +666,7 @@ int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>>>>       }
>>>>
>>>>       obj = container_of(node, struct drm_gem_object, vma_node);
>>>> -     ret = drm_gem_mmap_obj(obj, drm_vma_node_size(node), vma);
>>>> +     ret = drm_gem_mmap_obj(obj, drm_vma_node_size(node) << PAGE_SHIFT, vma);
>>>>
>>>>       mutex_unlock(&dev->struct_mutex);
>>>>
>>>> --
>>>> 1.8.3.4
>>>>
>>>
>>> --
>>> Daniel Vetter
>>> Software Engineer, Intel Corporation
>>> +41 (0) 79 365 57 48 - http://blog.ffwll.ch