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SubjectRe: [PATCH 4/4] drm/virtio: Add memory barriers for capset cache.
On Wed, Jun 05, 2019 at 04:44:23PM -0700, davidriley@chromium.org wrote:
> From: David Riley <davidriley@chromium.org>
>
> After data is copied to the cache entry, atomic_set is used indicate
> that the data is the entry is valid without appropriate memory barriers.
> Similarly the read side was missing the same memory barries.
>
> Signed-off-by: David Riley <davidriley@chromium.org>
> ---
> drivers/gpu/drm/virtio/virtgpu_ioctl.c | 3 +++
> drivers/gpu/drm/virtio/virtgpu_vq.c | 2 ++
> 2 files changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> index 88c1ed57a3c5..502f5f7c2298 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> @@ -542,6 +542,9 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
> if (!ret)
> return -EBUSY;
>
> + /* is_valid check must proceed before copy of the cache entry. */
> + virt_rmb();

I don't think you need virt_rmb() here. This isn't guest <=> host
communication, so a normal barrier should do.

The other three fixes are queued up for drm-misc-next.

cheers,
Gerd

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