[PATCH v2] drm: Set vm_ops to GEM object's values during mmap

[Thomas Zimmermann]

Hi

Am 15.01.21 um 15:11 schrieb Daniel Vetter:
> On Fri, Jan 15, 2021 at 09:57:24AM +0000, Kieran Bingham wrote:
>> Hi Thomas,
>>
>> On 15/01/2021 09:30, Thomas Zimmermann wrote:
>>> The GEM mmap code relies on the GEM object's mmap callback to set the
>>> VMA's vm_ops field. This is easily forgotten and already led to a memory
>>> leak in the CMA helpers. Instead set the vm_ops field in the DRM core
>>> code to the GEM object's value. Drivers with different needs can override
>>> this in their mmap callback.
>>>
>>> v2:
>>> 	* support (vm_ops == NULL) if mmap is given; required by VRAM
>>> 	  helpers
> 
> I guess vram helpers need this because ttm has it's own vm_ops struct?
> Might be another thing worth unifying (eventually).

I've been working on converting drivers to struct 
drm_gem_object_funcs.mmap and using DRM helpers for the other mmap 
callbacks. Part of this would include some unifying of the vm_ops 
handling. TTM drivers are kind of special here.

Best regards
Thomas

> 
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>>> Fixes: f5ca8eb6f9bd ("drm/cma-helper: Implement mmap as GEM CMA object functions")
>>> Reported-by: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
>>> Tested-by: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
>>
>> Re-tested just fine this side ;-)
>>   - https://paste.ubuntu.com/p/Jgz6xMKNJX/
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
>>
>> Thanks
>>
>> Kieran
>>
>>> Cc: Maxime Ripard <mripard at kernel.org>
>>> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>>> Cc: David Airlie <airlied at linux.ie>
>>> Cc: Daniel Vetter <daniel at ffwll.ch>
>>> Cc: Eric Anholt <eric at anholt.net>
>>> Cc: dri-devel at lists.freedesktop.org
>>> ---
>>>   drivers/gpu/drm/drm_gem.c   | 19 ++++++++++---------
>>>   drivers/gpu/drm/drm_prime.c |  2 ++
>>>   2 files changed, 12 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>> index 34b2f111c01c..c2ce78c4edc3 100644
>>> --- a/drivers/gpu/drm/drm_gem.c
>>> +++ b/drivers/gpu/drm/drm_gem.c
>>> @@ -1068,20 +1068,17 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
>>>   	drm_gem_object_get(obj);
>>>   
>>>   	vma->vm_private_data = obj;
>>> +	vma->vm_ops = obj->funcs->vm_ops;
>>>   
>>>   	if (obj->funcs->mmap) {
>>>   		ret = obj->funcs->mmap(obj, vma);
>>> -		if (ret) {
>>> -			drm_gem_object_put(obj);
>>> -			return ret;
>>> -		}
>>> +		if (ret)
>>> +			goto err_drm_gem_object_put;
>>>   		WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));
>>>   	} else {
>>> -		if (obj->funcs->vm_ops)
>>> -			vma->vm_ops = obj->funcs->vm_ops;
>>> -		else {
>>> -			drm_gem_object_put(obj);
>>> -			return -EINVAL;
>>> +		if (!vma->vm_ops) {
>>> +			ret = -EINVAL;
>>> +			goto err_drm_gem_object_put;
>>>   		}
>>>   
>>>   		vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
>>> @@ -1090,6 +1087,10 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
>>>   	}
>>>   
>>>   	return 0;
>>> +
>>> +err_drm_gem_object_put:
>>> +	drm_gem_object_put(obj);
>>> +	return ret;
>>>   }
>>>   EXPORT_SYMBOL(drm_gem_mmap_obj);
>>>   
>>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
>>> index 683aa29ecd3b..2a54f86856af 100644
>>> --- a/drivers/gpu/drm/drm_prime.c
>>> +++ b/drivers/gpu/drm/drm_prime.c
>>> @@ -717,6 +717,8 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
>>>   	vma->vm_pgoff += drm_vma_node_start(&obj->vma_node);
>>>   
>>>   	if (obj->funcs && obj->funcs->mmap) {
>>> +		vma->vm_ops = obj->funcs->vm_ops;
>>> +
> 
> Do you know how much we still need the non-obj->funcs path here? Maybe
> time to detele it and wrape the obj->funcs check in a WARN_ON?
> -Daniel
> 
> 
>>>   		ret = obj->funcs->mmap(obj, vma);
>>>   		if (ret)
>>>   			return ret;
>>>
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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