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SubjectRe: [PATCH] drm/virtio: fix mmap page attributes
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Hi

Am 10.12.19 um 09:57 schrieb Gerd Hoffmann:
> virtio-gpu uses cached mappings. shmem helpers use writecombine though.
> So roll our own mmap function, wrapping drm_gem_shmem_mmap(), to tweak
> vm_page_prot accordingly.
>
> Reported-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> drivers/gpu/drm/virtio/virtgpu_object.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 017a9e0fc3bb..158610902054 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -75,6 +75,22 @@ static void virtio_gpu_free_object(struct drm_gem_object *obj)
> drm_gem_shmem_free_object(obj);
> }
>
> +static int virtio_gpu_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> +{
> + pgprot_t prot;
> + int ret;
> +
> + ret = drm_gem_shmem_mmap(obj, vma);
> + if (ret < 0)
> + return ret;
> +
> + /* virtio-gpu needs normal caching, so clear writecombine */
> + prot = vm_get_page_prot(vma->vm_flags);
> + prot = pgprot_decrypted(prot);
> + vma->vm_page_prot = prot;
> + return 0;
> +}

There's similar code in udl, [1] which still uses writecombine for
imported buffers. Virtio does not need this?

Aside from this, do you think we could handle all special cases within
shmem?

Best regards
Thomas

[1]
https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/udl/udl_gem.c?id=28ecf94a6f1072fc4744c06f5b3d267297125b37#n20

> +
> static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .free = virtio_gpu_free_object,
> .open = virtio_gpu_gem_object_open,
> @@ -86,7 +102,7 @@ static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .get_sg_table = drm_gem_shmem_get_sg_table,
> .vmap = drm_gem_shmem_vmap,
> .vunmap = drm_gem_shmem_vunmap,
> - .mmap = &drm_gem_shmem_mmap,
> + .mmap = &virtio_gpu_gem_mmap,
> };
>
> struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
>

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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