[Qemu-devel] [PATCH] virtio_rpmsg: set DRIVER_OK before using device

[Michael S. Tsirkin]

virtio spec requires that all drivers set DRIVER_OK
before using devices. While rpmsg isn't yet
included in the virtio 1 spec, previous spec versions
also required this.

virtio rpmsg violates this rule: is calls kick
before setting DRIVER_OK.

The fix isn't trivial since simply calling virtio_device_ready earlier
would mean we might get an interrupt in parallel with adding buffers.

Instead, split kick out to prepare+notify calls.  prepare before
virtio_device_ready - when we know we won't get interrupts. notify right
afterwards.

Signed-off-by: Michael S. Tsirkin <address@hidden>
---

Note: compile-tested only.

 drivers/rpmsg/virtio_rpmsg_bus.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
index 92f6af6..73354ee 100644
--- a/drivers/rpmsg/virtio_rpmsg_bus.c
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -951,6 +951,7 @@ static int rpmsg_probe(struct virtio_device *vdev)
        void *bufs_va;
        int err = 0, i;
        size_t total_buf_space;
+       bool notify;
 
        vrp = kzalloc(sizeof(*vrp), GFP_KERNEL);
        if (!vrp)
@@ -1030,8 +1031,22 @@ static int rpmsg_probe(struct virtio_device *vdev)
                }
        }
 
+       /*
+        * Prepare to kick but don't notify yet - we can't do this before
+        * device is ready.
+        */
+       notify = virtqueue_kick_prepare(vrp->rvq);
+
+       /* From this point on, we can notify and get callbacks. */
+       virtio_device_ready(vdev);
+
        /* tell the remote processor it can start sending messages */
-       virtqueue_kick(vrp->rvq);
+       /*
+        * this might be concurrent with callbacks, but we are only
+        * doing notify, not a full kick here, so that's ok.
+        */
+       if (notify)
+               virtqueue_notify(vrp->rvq);
 
        dev_info(&vdev->dev, "rpmsg host is online\n");
 
-- 
MST