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

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 17 Apr 2025 10:53:23 +0100
Matthew Auld <matthew.auld@intel.com> wrote:

> 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@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?

We certainly are, good catch!

> 
> > +
> >   	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,  
>