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

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Date:   Tue, 15 Sep 2020 12:39:39 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Christian König <ckoenig.leichtzumerken@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, Linux MM <linux-mm@...ck.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/shmem-helpers: revert "Redirect mmap for imported dma-buf"

On Mon, Sep 14, 2020 at 3:29 PM Christian König
<ckoenig.leichtzumerken@...il.com> 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@....com>

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.

Also commit message should probably explain a bit the context here,
not a lot of people have been in our private discussion on this.
-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
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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