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Subject[PATCH 4.9 170/223] drm/virtio: Add memory barriers for capset cache.
Date
[ 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>
---
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 54639395aba0..a3559b1a3a0f 100644
--- 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 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


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