[PATCH v2] hw/virtio: propagate vhost_virtqueue_mask() errors from start path

[PATCH v2] hw/virtio: propagate vhost_virtqueue_mask() errors from start path

[Bin Guo]

vhost_virtqueue_start() unmasks the call notifier by calling
vhost_virtqueue_mask(), whose vhost_set_vring_call ioctl can fail
(closed vhost-user socket, kernel ENOMEM, revoked guest_notifier fd)
but whose void signature throws the error away. vhost_dev_start()
then reports success while the backend has no valid call eventfd for
that vq, leaving the guest with a working kick path but no virtqueue
interrupts -- a half-up state harder to diagnose than a clean failure.

Make vhost_virtqueue_mask() return int and handle the error in the
start path via the existing fail unwind. Other callers reach the
function through VirtioDeviceClass.guest_notifier_mask, whose void
signature offers no upward error channel; they invoke it as a
statement and remain unchanged.

Signed-off-by: Bin Guo <guobin@linux.alibaba.com>
---
 hw/virtio/vhost.c         | 9 ++++++---
 include/hw/virtio/vhost.h | 2 +-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index af41841b52..ad22c37c33 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1470,8 +1470,10 @@ int vhost_virtqueue_start(struct vhost_dev *dev,
      * will do it later.
      */
     if (!vdev->use_guest_notifier_mask) {
-        /* TODO: check and handle errors. */
-        vhost_virtqueue_mask(dev, vdev, idx, false);
+        r = vhost_virtqueue_mask(dev, vdev, idx, false);
+        if (r < 0) {
+            goto fail;
+        }
     }
 
     if (k->query_guest_notifiers &&
@@ -1918,7 +1920,7 @@ bool vhost_virtqueue_pending(struct vhost_dev *hdev, int n)
 }
 
 /* Mask/unmask events from this vq. */
-void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
+int vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
                          bool mask)
 {
     struct VirtQueue *vvq = virtio_get_queue(vdev, n);
@@ -1940,6 +1942,7 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
     if (r < 0) {
         error_report("vhost_set_vring_call failed %d", -r);
     }
+    return r;
 }
 
 bool vhost_config_pending(struct vhost_dev *hdev)
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 684bafcaad..1f62332d60 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -312,7 +312,7 @@ bool vhost_virtqueue_pending(struct vhost_dev *hdev, int n);
 
 /* Mask/unmask events from this vq.
  */
-void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
+int vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
                           bool mask);
 
 /**
-- 
2.50.1 (Apple Git-155)