From: Marc-André Lureau <marcandre.lur...@redhat.com>
vhost switches between masked notifier and guest notifier when
unmasking. virtio_pci_vq_vector_unmask() checks if there was pending
notification, but at the time it is checked, vhost-user backend doesn't
guarantee that the switch happened yet, so it may lose some events.
To solve this vhost-user race, I introduced an extra "sync"
call (waiting for a reply). One may want to make all/many vhost-user
replies mandatories by adding a new capability instead.
Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
---
hw/virtio/vhost.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 4400718..692c38f 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1181,6 +1181,7 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev,
VirtIODevice *vdev, int n,
struct VirtQueue *vvq = virtio_get_queue(vdev, n);
int r, index = n - hdev->vq_index;
struct vhost_vring_file file;
+ uint64_t features;
if (mask) {
assert(vdev->use_guest_notifier_mask);
@@ -1192,6 +1193,10 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev,
VirtIODevice *vdev, int n,
file.index = hdev->vhost_ops->vhost_get_vq_index(hdev, n);
r = hdev->vhost_ops->vhost_set_vring_call(hdev, &file);
assert(r >= 0);
+
+ /* silly sync call to make sure the call fd has been received */
+ r = hdev->vhost_ops->vhost_get_features(hdev, &features);
+ assert(r >= 0);
}
uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
--
2.7.4
