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

From: Daniel Vetter <daniel@ffwll.ch>
To: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Gerd Hoffmann <kraxel@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 8/9] drm/shmem-helpers: Ensure get_pages is not called on imported dma-buf
Date: Mon, 8 Jun 2020 17:04:10 +0200	[thread overview]
Message-ID: <20200608150410.GY20149@phenom.ffwll.local> (raw)
In-Reply-To: <37f561a1-c0fc-57c9-4759-9fca5ae46a4d@suse.de>

On Mon, Jun 08, 2020 at 04:40:26PM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 03.06.20 um 15:12 schrieb Daniel Vetter:
> > 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.
> 
> Thanks for explaining. Patch is

Thanks for taking a look at all this, last 2 patches now also merged to
drm-misc-next.
-Daniel

> 
> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
> 
> > 
> > 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
> >>
> > 
> > 
> > 
> > 
> 
> -- 
> 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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