Linux Virtualization - Jul 2019 - [PATCH AUTOSEL 4.4 10/35] drm/virtio: Add memory barriers for capset cache.

From: David Riley <davidriley at chromium.org>

[ 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 at chromium.org>
Link:
http://patchwork.freedesktop.org/patch/msgid/20190610211810.253227-5-davidriley
at chromium.org
Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
Signed-off-by: Sasha Levin <sashal at kernel.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 6296e9f270ca..0b8f8c10f2ed 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -535,6 +535,9 @@ 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 52436b3c01bb..a1b3ea1ccb65 100644
--- 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;
 		}
-- 
2.20.1