drm/virtio: Add memory barriers for capset cache.

[ Upstream commit 9ff3a5c88e1f1ab17a31402b96d45abe14aab9d7 ]

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 corresponding memory barriers.

Signed-off-by: David Riley <davidriley@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20190610211810.253227-5-davidriley@chromium.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 5463939..a3559b1 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -521,6 +521,9 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
        ret = wait_event_timeout(vgdev->resp_wq,
                                 atomic_read(&cache_ent->is_valid), 5 * HZ);
 
+       /* is_valid check must proceed before copy of the cache entry. */
+       smp_rmb();
+
        ptr = cache_ent->caps_cache;
 
 copy_exit:

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 52436b3..a1b3ea1 100644 (file)
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -618,6 +618,8 @@ static void virtio_gpu_cmd_capset_cb(struct virtio_gpu_device *vgdev,
                    cache_ent->id == le32_to_cpu(cmd->capset_id)) {
                        memcpy(cache_ent->caps_cache, resp->capset_data,
                               cache_ent->size);
+                       /* Copy must occur before is_valid is signalled. */
+                       smp_wmb();
                        atomic_set(&cache_ent->is_valid, 1);
                        break;
                }