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

Daniel Vetter daniel.vetter at ffwll.ch
Mon May 11 09:35:46 UTC 2020

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.

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)
 	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:

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