On Mon, May 11, 2020 at 2:36 AM Daniel Vetter <daniel.vetter@xxxxxxxx> 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.
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@xxxxxxxxx>
> Cc: Rob Clark <robdclark@xxxxxxxxx>
> Cc: Sean Paul <sean@xxxxxxxxxx>
> Cc: linux-arm-msm@xxxxxxxxxxxxxxx
> Cc: freedreno@xxxxxxxxxxxxxxxxxxxxx
> ---
> 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
>
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