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virtio: introduce grab/release_ioeventfd to fix vhost

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Following the recent refactoring of virtio notifiers [1], more specifically
the patch ed08a2a0b ("virtio: use virtio_bus_set_host_notifier to
start/stop ioeventfd") 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.

When vhost is stopped and started, however, there is 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 reintroduces (hopefully in a cleaner way) the concept
that was present with ioeventfd_disabled before the refactoring.
When ioeventfd_grabbed>0, ioeventfd_started tracks whether ioeventfd
should be enabled or not, but ioeventfd is actually not started at
all until vhost releases the host notifiers.

[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

Reported-by: Felipe Franciosi <felipe@nutanix.com>
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reported-by: Alex Williamson <alex.williamson@redhat.com>
Fixes: ed08a2a0b ("virtio: use virtio_bus_set_host_notifier to start/stop ioeventfd")
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Tested-by: Farhan Ali <alifm@linux.vnet.ibm.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-11-18 16:07:00 +01:00 • committed by Michael S. Tsirkin
parent 600f5ce356
commit 310837de6c
5 changed files with 86 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

16
hw/virtio/virtio.c
View file

@ -2191,6 +2191,22 @@ void virtio_device_stop_ioeventfd(VirtIODevice *vdev)
virtio_bus_stop_ioeventfd(vbus);
}
int virtio_device_grab_ioeventfd(VirtIODevice *vdev)
{
BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
VirtioBusState *vbus = VIRTIO_BUS(qbus);
return virtio_bus_grab_ioeventfd(vbus);
}
void virtio_device_release_ioeventfd(VirtIODevice *vdev)
{
BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
VirtioBusState *vbus = VIRTIO_BUS(qbus);
virtio_bus_release_ioeventfd(vbus);
}
static void virtio_device_class_init(ObjectClass *klass, void *data)
{
/* Set the default value here. */