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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, we 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_vunmap is the wrong thing to do.
v2: Rob said in review that we do indeed have a gap in get_vaddr() that
needs to be plugged. But the users I've found aren't legit users on
imported dma-buf, so we can just reject that.
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200514201117.465146-1-daniel.vetter@ffwll.ch
8b6b7d84bf