[Qemu-devel] [PATCH] vhost-scsi: 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. Since vhost-scsi uses the legacy
interface, this value is not updated.

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 module 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
---
 hw/scsi/vhost-scsi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
index 5b26946..1c6e6d4 100644
--- a/hw/scsi/vhost-scsi.c
+++ b/hw/scsi/vhost-scsi.c
@@ -95,6 +95,7 @@ static int vhost_scsi_start(VHostSCSI *s)
     if (ret < 0) {
         return ret;
     }
+    VIRTIO_BUS(qbus)->ioeventfd_started = true;
 
     s->dev.acked_features = vdev->guest_features;
     ret = vhost_dev_start(&s->dev, vdev);
@@ -152,6 +153,7 @@ static void vhost_scsi_stop(VHostSCSI *s)
     vhost_scsi_clear_endpoint(s);
     vhost_dev_stop(&s->dev, vdev);
     vhost_dev_disable_notifiers(&s->dev, vdev);
+    VIRTIO_BUS(qbus)->ioeventfd_started = false;
 }
 
 static uint64_t vhost_scsi_get_features(VirtIODevice *vdev,
-- 
1.9.4