Re: [PATCH 8/9] drm/shmem-helpers: Ensure get_pages is not called on imported dma-buf

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, May 14, 2020 at 09:30:04AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 11.05.20 um 11:35 schrieb Daniel Vetter:
> > Just a bit of light paranoia. Also sprinkle this check over
> > drm_gem_shmem_get_sg_table, which should only be called when
> > exporting, same for the pin/unpin functions, on which it relies to
> > work correctly.
> > 
> > Cc: Gerd Hoffmann <kraxel@redhat.com>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Noralf Trønnes <noralf@tronnes.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >  drivers/gpu/drm/drm_gem_shmem_helper.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index 117a7841e284..f7011338813e 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -170,6 +170,8 @@ int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> >  {
> >  	int ret;
> >  
> > +	WARN_ON(shmem->base.import_attach);
> > +
> >  	ret = mutex_lock_interruptible(&shmem->pages_lock);
> >  	if (ret)
> >  		return ret;
> > @@ -225,6 +227,8 @@ int drm_gem_shmem_pin(struct drm_gem_object *obj)
> >  {
> >  	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >  
> > +	WARN_ON(shmem->base.import_attach);
> > +
> 
> I don't understand this change. If a driver pins pages it now has to
> check that the pages are not imported?

Nope. There's two classes of functions in the helpers, and I'm trying to
unconfuse them:

- stuff used to implement gem_funcs. These are obviously only ever used on
  native objects, never on imported ones (on imported ones we try to
  forward through the dma-buf layer to the exporter). drm_gem_shmem_pin is
  only used in that role to implement gem_funcs->pin. Calling it on an
  imported buffer is indeed a bug.

- the other set of functions are for drivers to do their stuff. The
  interface which (implicitly) pins stuff into places is various set of
  get_pages, which do have different paths for native and imported
  objects.

Apologies that I missed your question here, I merged all the patches
leading up to this one for now.

Thanks, Daniel

> 
> 
> >  	return drm_gem_shmem_get_pages(shmem);
> >  }
> >  EXPORT_SYMBOL(drm_gem_shmem_pin);
> > @@ -240,6 +244,8 @@ void drm_gem_shmem_unpin(struct drm_gem_object *obj)
> >  {
> >  	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >  
> > +	WARN_ON(shmem->base.import_attach);
> > +
> >  	drm_gem_shmem_put_pages(shmem);
> >  }
> >  EXPORT_SYMBOL(drm_gem_shmem_unpin);
> > @@ -510,6 +516,8 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
> >  	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >  	int ret;
> >  
> > +	WARN_ON(shmem->base.import_attach);
> > +
> >  	ret = drm_gem_shmem_get_pages(shmem);
> >  	WARN_ON_ONCE(ret != 0);
> >  
> > @@ -611,6 +619,8 @@ struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_object *obj)
> >  {
> >  	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> >  
> > +	WARN_ON(shmem->base.import_attach);
> > +
> >  	return drm_prime_pages_to_sg(shmem->pages, obj->size >> PAGE_SHIFT);
> >  }
> >  EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
> 




-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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