linux-kernel - [PATCH] drm/virtio: fix mmap page attributes

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Date:   Tue, 10 Dec 2019 09:57:59 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     gurchetansingh@...omium.org, Gerd Hoffmann <kraxel@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        virtualization@...ts.linux-foundation.org (open list:VIRTIO GPU DRIVER),
        linux-kernel@...r.kernel.org (open list)
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@...omium.org>
Signed-off-by: Gerd Hoffmann <kraxel@...hat.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;
+}
+
 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