Re: [PATCH 1/2] drm/shmem-helpers: revert "Redirect mmap for imported dma-buf"

[Christian König]

Am 15.09.20 um 12:39 schrieb Daniel Vetter:
> On Mon, Sep 14, 2020 at 3:29 PM Christian König
> <ckoenig.leichtzumerken@xxxxxxxxx> wrote:
> > This reverts commit 26d3ac3cb04d171a861952e89324e347598a347f.
> >
> > We need to figure out if dma_buf_mmap() is valid or not first.
> >
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> The trouble is that doing dma-buf mmap by looking at the struct pages
> behind the sg list and just inserting those into userspace doesn't
> really work any better. You still won't get the unmap_mapping_range
> and hence pte shoot-down. So maybe dma_buf_mmap forwarding doesn't
> work, but this doesn't make it any better.

Good point. Question is what should we do? Return -EPERM?

> Also commit message should probably explain a bit the context here,
> not a lot of people have been in our private discussion on this.

Well, that's certain true.

Christian.

> -Daniel
>
> > ---
> >   drivers/gpu/drm/drm_gem_shmem_helper.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > index 0a952f27c184..cd727343f72b 100644
> > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> > @@ -594,9 +594,6 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> >          /* Remove the fake offset */
> >          vma->vm_pgoff -= drm_vma_node_start(&obj->vma_node);
> >
> > -       if (obj->import_attach)
> > -               return dma_buf_mmap(obj->dma_buf, vma, 0);
> > -
> >          shmem = to_drm_gem_shmem_obj(obj);
> >
> >          ret = drm_gem_shmem_get_pages(shmem);
> > --
> > 2.17.1
> >
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