Re: [PATCH] drm/shmem-helper: Reset vma->vm_ops before calling dma_buf_mmap()

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Hi

Am 24.07.23 um 13:26 schrieb Boris Brezillon:
The dma-buf backend is supposed to provide its own vm_ops, but some
implementation just have nothing special to do and leave vm_ops
untouched, probably expecting this field to be zero initialized (this
is the case with the system_heap implementation for instance).
Let's reset vma->vm_ops to NULL to keep things working with these
implementations.

Thanks for your patch. This bug could affect a number of GEM implementations. Instead of fixing this individually, could we set the fields conditionally at


https://elixir.bootlin.com/linux/v6.4/source/drivers/gpu/drm/drm_gem.c#L1042

?

Something like

  if (!object->import_attach) {
    vma->priv =
    vma->ops =
  }

plus a descriptive comment like the one you have in your patch.

Best regards
Thomas


Fixes: 26d3ac3cb04d ("drm/shmem-helpers: Redirect mmap for imported dma-buf")
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Reported-by: Roman Stratiienko <roman.stratiienko@xxxxxxxxxxxxxxx>
Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
---
  drivers/gpu/drm/drm_gem_shmem_helper.c | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 4ea6507a77e5..baaf0e0feb06 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -623,7 +623,13 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
  	int ret;
if (obj->import_attach) {
+		/* Reset both vm_ops and vm_private_data, so we don't end up with
+		 * vm_ops pointing to our implementation if the dma-buf backend
+		 * doesn't set those fields.
+		 */
  		vma->vm_private_data = NULL;
+		vma->vm_ops = NULL;
+
  		ret = dma_buf_mmap(obj->dma_buf, vma, 0);
/* Drop the reference drm_gem_mmap_obj() acquired.*/

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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