On 5/27/22 01:50, Dmitry Osipenko wrote:
Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
handle imported dma-bufs properly, which results in mapping of something
else than the imported dma-buf. For example, on NVIDIA Tegra we get a hard
lockup when userspace writes to the memory mapping of a dma-buf that was
imported into Tegra's DRM GEM.
To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj().
Now mmaping of imported dma-bufs works properly for all DRM drivers.
Same comment about Fixes: as in patch 1,
Cc: sta...@vger.kernel.org
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
drivers/gpu/drm/drm_gem.c | 3 +++
drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
drivers/gpu/drm/tegra/gem.c | 4 ++++
3 files changed, 7 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 86d670c71286..7c0b025508e4 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned
long obj_size,
if (obj_size < vma->vm_end - vma->vm_start)
return -EINVAL;
+ if (obj->import_attach)
+ return dma_buf_mmap(obj->dma_buf, vma, 0);
If we start enabling mmaping of imported dma-bufs on a majority of
drivers in this way, how do we ensure that user-space is not blindly
using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
which is needed before and after cpu access of mmap'ed dma-bufs?
I was under the impression (admittedly without looking) that the few
drivers that actually called into dma_buf_mmap() had some private
user-mode driver code in place that ensured this happened.
/Thomas
+
/* Take a ref for this mapping of the object, so that the fault
* handler can dereference the mmap offset's pointer to the object.
* This reference is cleaned up by the corresponding vm_close
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 8ad0e02991ca..6190f5018986 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -609,17 +609,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
*/
int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct
vm_area_struct *vma)
{
- struct drm_gem_object *obj = &shmem->base;
int ret;
- if (obj->import_attach) {
- /* Drop the reference drm_gem_mmap_obj() acquired.*/
- drm_gem_object_put(obj);
- vma->vm_private_data = NULL;
-
- return dma_buf_mmap(obj->dma_buf, vma, 0);
- }
-
ret = drm_gem_shmem_get_pages(shmem);
if (ret) {
drm_gem_vm_close(vma);
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index 7c7dd84e6db8..f92aa20d63bb 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -564,6 +564,10 @@ int __tegra_gem_mmap(struct drm_gem_object *gem, struct
vm_area_struct *vma)
{
struct tegra_bo *bo = to_tegra_bo(gem);
+ /* imported dmu-buf is mapped by drm_gem_mmap_obj() */
+ if (gem->import_attach)
+ return 0;
+
if (!bo->pages) {
unsigned long vm_pgoff = vma->vm_pgoff;
int err;
