RE: [PATCH] drm/virtio: fix mmap page attributes

[Ruhl, Michael J]

>-----Original Message-----
>From: dri-devel <dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of
>Gerd Hoffmann
>Sent: Tuesday, December 10, 2019 3:58 AM
>To: dri-devel@xxxxxxxxxxxxxxxxxxxxx
>Cc: David Airlie <airlied@xxxxxxxx>; open list <linux-kernel@xxxxxxxxxxxxxxx>;
>open list:VIRTIO GPU DRIVER <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>;
>Gerd Hoffmann <kraxel@xxxxxxxxxx>; gurchetansingh@xxxxxxxxxxxx
>Subject: [PATCH] drm/virtio: fix mmap page attributes
>
>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@xxxxxxxxxxxx>
>Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
>---
> 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 */

A minor nit. 

I was looking at this code, trying to see where you were clearing the
writecombine bit.

Maybe a more clear comment would be:

virtio-gpu needs normal caching, re-do protection without writecombine

?

Mike

>+	prot = vm_get_page_prot(vma->vm_flags);
>+	prot = pgprot_decrypted(prot);
>+	vma->vm_page_prot = prot;
>+	return 0;
>+}
>+
> 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,
>--
>2.18.1
>
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