[Intel-gfx] [PATCH 1/9] drm/msm: Don't call dma_buf_vunmap without _vmap

[Rob Clark]

On Mon, May 11, 2020 at 8:29 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> On Mon, May 11, 2020 at 5:24 PM Rob Clark <robdclark at gmail.com> wrote:
> >
> > On Mon, May 11, 2020 at 2:36 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > >
> > > I honestly don't exactly understand what's going on here, but the
> > > current code is wrong for sure: It calls dma_buf_vunmap without ever
> > > calling dma_buf_vmap.
> > >
> > > What I'm not sure about is whether the WARN_ON is correct:
> > > - msm imports dma-buf using drm_prime_sg_to_page_addr_arrays. Which is
> > >   a pretty neat layering violation of how you shouldn't peek behind
> > >   the curtain of the dma-buf exporter, but par for course. Note that
> > >   all the nice new helpers don't (and we should probably have a bit a
> > >   warning about this in the kerneldoc).
> > >
> > > - but then in the get_vaddr() in msm_gem.c, and that seems to happily
> > >   wrap a vmap() around any object with ->pages set (so including
> > >   imported dma-buf)
> > >
> > > - I'm not seeing any guarantees that userspace can't use an imported
> > >   dma-buf for e.g. MSM_SUBMIT_CMD_BUF in a5xx_submit_in_rb, so no
> > >   guarantees that an imported dma-buf won't end up with a ->vaddr set.
> >
> > fwiw, a5xx_submit_in_rb() isn't a "normal" path (build-time disabled
> > by default, and restricted to sudo).. it really only exists to
> > simplify poking at fw.
> >
> > There could be vmap's in the msm_gem_submit path, however.  If we
> > don't, we should probably just disallow using an imported dma-buf as
> > cmdstream.. I don't think there is any sane reason to permit that.  We
> > should probably also disallow get_vaddr() on imported buffers.
>
> Yeah if that's possible and won't blow up (I can't test) I think it'd
> be best. Something like
> if (bo->import_attach) return NULL; should do the trick I think.
> Should I type that up as v2 of this?

Sure.  It should probably be something like

  if (obj->import_attach)
    return ERR_PTR(-ESOMETHING)

looks like the gem-submit path handles an IS_ERR() return

BR,
-R


> -Daniel
>
> >
> > BR,
> > -R
> >
> > >
> > > But even if that WARN_ON is wrong, cleaning up a vmap() done by msm by
> > > calling dma_buf_vmap is the wrong thing to do.
> > >
> > > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > > Cc: Rob Clark <robdclark at gmail.com>
> > > Cc: Sean Paul <sean at poorly.run>
> > > Cc: linux-arm-msm at vger.kernel.org
> > > Cc: freedreno at lists.freedesktop.org
> > > ---
> > >  drivers/gpu/drm/msm/msm_gem.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> > > index 5a6a79fbc9d6..3305a457960e 100644
> > > --- a/drivers/gpu/drm/msm/msm_gem.c
> > > +++ b/drivers/gpu/drm/msm/msm_gem.c
> > > @@ -907,8 +907,7 @@ static void free_object(struct msm_gem_object *msm_obj)
> > >         put_iova(obj);
> > >
> > >         if (obj->import_attach) {
> > > -               if (msm_obj->vaddr)
> > > -                       dma_buf_vunmap(obj->import_attach->dmabuf, msm_obj->vaddr);
> > > +               WARN_ON(msm_obj->vaddr);
> > >
> > >                 /* Don't drop the pages for imported dmabuf, as they are not
> > >                  * ours, just free the array we allocated:
> > > --
> > > 2.26.2
> > >
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch