[Qemu-devel] [PATCH v2] vhost: Update 'ioeventfd_started' with host notifiers

[Felipe Franciosi <felipe@nutanix.com>]

Following the recent refactor of virtio notfiers [1], more specifically
the patch that uses virtio_bus_set_host_notifier [2] by default, core
virtio code requires 'ioeventfd_started' to be set to true/false when
the host notifiers are configured. Because not all vhost devices were
update (eg. vhost-scsi) to use the new interface, this value is always
set to false.

When booting a guest with a vhost-scsi backend controller, SeaBIOS will
initially configure the device which sets all notifiers. The guest will
continue to boot fine until the kernel virtio-scsi driver reinitialises
the device causing a stop followed by another start. Since
ioeventfd_started was never set to true, the 'stop' operation triggered
by virtio_bus_set_host_notifier() will not result in a call to
virtio_pci_ioeventfd_assign(assign=false). This leaves the memory
regions with stale notifiers and results on the next start triggering
the following assertion:

  kvm_mem_ioeventfd_add: error adding ioeventfd: File exists
  Aborted

This patch updates ioeventfd_started whenever the notifiers are set or
cleared, fixing this issue.

Signed-off-by: Felipe Franciosi <felipe@nutanix.com>

[1] http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg07748.html
[2] http://lists.nongnu.org/archive/html/qemu-devel/2016-10/msg07760.html
---
 v1->v2:
  - Update ioeventfd_started in vhost_dev_enable/disable_notifiers()
    instead of vhost_scsi_start/stop().
  - Reword the commit message accordingly.
---
 hw/virtio/vhost.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 131f164..1290963 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1205,6 +1205,7 @@ int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
             goto fail_vq;
         }
     }
+    VIRTIO_BUS(qbus)->ioeventfd_started = true;
 
     return 0;
 fail_vq:
@@ -1239,6 +1240,7 @@ void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev)
         }
         assert (r >= 0);
     }
+    VIRTIO_BUS(qbus)->ioeventfd_started = false;
     virtio_device_start_ioeventfd(vdev);
 }
 
-- 
1.9.4