[PATCH v2] drm/panthor: Don't create a file offset for NO_MMAP BOs

[Matthew Auld]

On 17/04/2025 10:32, Boris Brezillon wrote:
> Right now the DRM_PANTHOR_BO_NO_MMAP flag is ignored by
> panthor_ioctl_bo_mmap_offset(), meaning BOs with this flag set can
> have a file offset but can't be mapped anyway, because
> panthor_gem_mmap() will filter them out.
> 
> If we error out at mmap_offset creation time, we can get rid of
> panthor_gem_mmap() and call drm_gem_shmem_object_mmap directly, and
> we get rid of this inconsistency of having an mmap offset for a
> BO that can never be mmap-ed.
> 
> Changes in v2:
> - Get rid of panthor_gem_mmap()
> - Get rid of the Fixes tag and adjust the commit message accordingly
> - Return ENOPERM instead of EINVAL
> 
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> ---
>   drivers/gpu/drm/panthor/panthor_drv.c |  5 +++++
>   drivers/gpu/drm/panthor/panthor_gem.c | 13 +------------
>   2 files changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> index 06fe46e32073..7cd131af340d 100644
> --- a/drivers/gpu/drm/panthor/panthor_drv.c
> +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> @@ -940,6 +940,7 @@ static int panthor_ioctl_bo_mmap_offset(struct drm_device *ddev, void *data,
>   					struct drm_file *file)
>   {
>   	struct drm_panthor_bo_mmap_offset *args = data;
> +	struct panthor_gem_object *bo;
>   	struct drm_gem_object *obj;
>   	int ret;
>   
> @@ -950,6 +951,10 @@ static int panthor_ioctl_bo_mmap_offset(struct drm_device *ddev, void *data,
>   	if (!obj)
>   		return -ENOENT;
>   
> +	bo = to_panthor_bo(obj);
> +	if (bo->flags & DRM_PANTHOR_BO_NO_MMAP)
> +		return -EPERM;

Just a drive-by-comment: are we not leaking the bo ref here?

> +
>   	ret = drm_gem_create_mmap_offset(obj);
>   	if (ret)
>   		goto out;
> diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c
> index fd014ccc3bfc..22d78cef9c66 100644
> --- a/drivers/gpu/drm/panthor/panthor_gem.c
> +++ b/drivers/gpu/drm/panthor/panthor_gem.c
> @@ -129,17 +129,6 @@ panthor_kernel_bo_create(struct panthor_device *ptdev, struct panthor_vm *vm,
>   	return ERR_PTR(ret);
>   }
>   
> -static int panthor_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> -{
> -	struct panthor_gem_object *bo = to_panthor_bo(obj);
> -
> -	/* Don't allow mmap on objects that have the NO_MMAP flag set. */
> -	if (bo->flags & DRM_PANTHOR_BO_NO_MMAP)
> -		return -EINVAL;
> -
> -	return drm_gem_shmem_object_mmap(obj, vma);
> -}
> -
>   static struct dma_buf *
>   panthor_gem_prime_export(struct drm_gem_object *obj, int flags)
>   {
> @@ -169,7 +158,7 @@ static const struct drm_gem_object_funcs panthor_gem_funcs = {
>   	.get_sg_table = drm_gem_shmem_object_get_sg_table,
>   	.vmap = drm_gem_shmem_object_vmap,
>   	.vunmap = drm_gem_shmem_object_vunmap,
> -	.mmap = panthor_gem_mmap,
> +	.mmap = drm_gem_shmem_object_mmap,
>   	.status = panthor_gem_status,
>   	.export = panthor_gem_prime_export,
>   	.vm_ops = &drm_gem_shmem_vm_ops,