Re: [PATCH v3 1/2] drm/gem: drm_gem_dumb_map_offset(): reject dma-buf

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Laurent Pinchart (2017-08-17 20:01:40)
> Hi Chris,
> 
> On Thursday 17 Aug 2017 19:30:44 Chris Wilson wrote:
> > Quoting Laurent Pinchart (2017-08-17 18:56:09)
> > > On Thursday 17 Aug 2017 18:21:30 Noralf Trønnes wrote:
> > > > Reject mapping an imported dma-buf since is's an invalid use-case.
> > > > 
> > > > Cc: Philipp Zabel <p.zabel@pengutronix.de>
> > > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > Cc: Sean Paul <seanpaul@chromium.org>
> > > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > > Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> > > > ---
> > > > 
> > > >  drivers/gpu/drm/drm_gem.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> > > > index ad4e9cf..8da5801 100644
> > > > --- a/drivers/gpu/drm/drm_gem.c
> > > > +++ b/drivers/gpu/drm/drm_gem.c
> > > > @@ -333,6 +333,12 @@ int drm_gem_dumb_map_offset(struct drm_file *file,
> > > > struct drm_device *dev, if (!obj)
> > > > 
> > > >               return -ENOENT;
> > > > 
> > > > +     /* Don't allow imported objects to be mapped */
> > > > +     if (obj->import_attach) {
> > > > +             ret = -EINVAL;
> > > > +             goto out;
> > > > +     }
> > > > +
> > > 
> > > Wouldn't it be better to move this check to
> > > drm_gem_create_mmap_offset_size() to reject mapping of all imported
> > > dmabuf, not just the ones associated with dumb buffers ?
> > 
> > No, we use that and we don't ban mapping an imported object.
> 
> Do you use that with driver-specific buffers only or with dumb buffers too ?

For dma-buf we import? The current presumption is that the sg_table is
backed by struct page. How would we know otherwise? I am actually not
sure what would happen if we tried to use another mmio bar from the GPU.

For dumb buffers we create, they are just ordinary buffers.
-Chris
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