The BOs created with DRM_PANTHOR_BO_NO_MMAP flag are not supposed to be
mmappable by the Userspace. But after the rework to support shrinker,
it became possible to mmap NO_MMAP BOs. Userspace could second guess
the file offset range, allocated unconditionally at the BO creation
time, and create a CPU mapping. There may not be any adverse effect of
such a CPU mapping though.
This commit removes the unconditional allocation of file offset range
when a user/kernel BO is created. For user BOs, allocation of file
offset range would be done from BO_MMAP_OFFSET ioctl handler which has
a check for NO_MMAP flag. For kernel BOs, there is no need to allocate
file offset range.

Fixes: 68cbf96b1e9b ("drm/panthor: Part ways with drm_gem_shmem_object")
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Akash Goel <akash.goel@arm.com>
---
 drivers/gpu/drm/panthor/panthor_gem.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
index c07a44057e42..5cfe66537e87 100644
--- a/drivers/gpu/drm/panthor/panthor_gem.c
+++ b/drivers/gpu/drm/panthor/panthor_gem.c
@@ -1021,10 +1021,6 @@ panthor_gem_create(struct drm_device *dev, size_t size, uint32_t flags,
 	mapping_set_gfp_mask(bo->base.filp->f_mapping,
 			     GFP_HIGHUSER | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
 
-	ret = drm_gem_create_mmap_offset(&bo->base);
-	if (ret)
-		goto err_put;
-
 	if (exclusive_vm) {
 		bo->exclusive_vm_root_gem = panthor_vm_root_gem(exclusive_vm);
 		drm_gem_object_get(bo->exclusive_vm_root_gem);
-- 
2.25.1

On Tue, Sep 22, 2026 at 11:07:43AM +0100, Akash Goel wrote:
> The BOs created with DRM_PANTHOR_BO_NO_MMAP flag are not supposed to be
> mmappable by the Userspace. But after the rework to support shrinker,
> it became possible to mmap NO_MMAP BOs. Userspace could second guess
> the file offset range, allocated unconditionally at the BO creation
> time, and create a CPU mapping. There may not be any adverse effect of
> such a CPU mapping though.
> This commit removes the unconditional allocation of file offset range
> when a user/kernel BO is created. For user BOs, allocation of file
> offset range would be done from BO_MMAP_OFFSET ioctl handler which has
> a check for NO_MMAP flag. For kernel BOs, there is no need to allocate
> file offset range.
> 
> Fixes: 68cbf96b1e9b ("drm/panthor: Part ways with drm_gem_shmem_object")
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Akash Goel <akash.goel@arm.com>

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Best regards,
Liviu

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index c07a44057e42..5cfe66537e87 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -1021,10 +1021,6 @@ panthor_gem_create(struct drm_device *dev, size_t size, uint32_t flags,
>  	mapping_set_gfp_mask(bo->base.filp->f_mapping,
>  			     GFP_HIGHUSER | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>  
> -	ret = drm_gem_create_mmap_offset(&bo->base);
> -	if (ret)
> -		goto err_put;
> -
>  	if (exclusive_vm) {
>  		bo->exclusive_vm_root_gem = panthor_vm_root_gem(exclusive_vm);
>  		drm_gem_object_get(bo->exclusive_vm_root_gem);
> -- 
> 2.25.1
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

On Tue, 22 Sep 2026 11:07:43 +0100
Akash Goel <akash.goel@arm.com> wrote:

> The BOs created with DRM_PANTHOR_BO_NO_MMAP flag are not supposed to be
> mmappable by the Userspace. But after the rework to support shrinker,
> it became possible to mmap NO_MMAP BOs. Userspace could second guess
> the file offset range, allocated unconditionally at the BO creation
> time, and create a CPU mapping. There may not be any adverse effect of
> such a CPU mapping though.
> This commit removes the unconditional allocation of file offset range
> when a user/kernel BO is created. For user BOs, allocation of file
> offset range would be done from BO_MMAP_OFFSET ioctl handler which has
> a check for NO_MMAP flag. For kernel BOs, there is no need to allocate
> file offset range.
> 
> Fixes: 68cbf96b1e9b ("drm/panthor: Part ways with drm_gem_shmem_object")
> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
> Signed-off-by: Akash Goel <akash.goel@arm.com>

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>

> ---
>  drivers/gpu/drm/panthor/panthor_gem.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index c07a44057e42..5cfe66537e87 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -1021,10 +1021,6 @@ panthor_gem_create(struct drm_device *dev, size_t size, uint32_t flags,
>  	mapping_set_gfp_mask(bo->base.filp->f_mapping,
>  			     GFP_HIGHUSER | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>  
> -	ret = drm_gem_create_mmap_offset(&bo->base);
> -	if (ret)
> -		goto err_put;
> -
>  	if (exclusive_vm) {
>  		bo->exclusive_vm_root_gem = panthor_vm_root_gem(exclusive_vm);
>  		drm_gem_object_get(bo->exclusive_vm_root_gem);