On Thu, May 14, 2020 at 1:11 PM Daniel Vetter daniel.vetter@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, 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.
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
Reviewed-by: Rob Clark robdclark@gmail.com
drivers/gpu/drm/msm/msm_gem.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c index 5a6a79fbc9d6..e70abd1cde43 100644 --- a/drivers/gpu/drm/msm/msm_gem.c +++ b/drivers/gpu/drm/msm/msm_gem.c @@ -554,6 +554,9 @@ static void *get_vaddr(struct drm_gem_object *obj, unsigned madv) struct msm_gem_object *msm_obj = to_msm_bo(obj); int ret = 0;
if (obj->import_attach)return ERR_PTR(-ENODEV);mutex_lock(&msm_obj->lock); if (WARN_ON(msm_obj->madv > madv)) {@@ -907,8 +910,7 @@ 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