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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

14
include/hw/virtio/virtio-bus.h
View file

@ -97,6 +97,16 @@ struct VirtioBusState {
* Set if ioeventfd has been started.
*/
bool ioeventfd_started;
/*
* Set if ioeventfd has been grabbed by vhost. When ioeventfd
* is grabbed by vhost, we track its started/stopped state (which
* depends in turn on the virtio status register), but do not
* register a handler for the ioeventfd. When ioeventfd is
* released, if ioeventfd_started is true we finally register
* the handler so that QEMU's device model can use ioeventfd.
*/
int ioeventfd_grabbed;
};
void virtio_bus_device_plugged(VirtIODevice *vdev, Error **errp);
@ -131,6 +141,10 @@ bool virtio_bus_ioeventfd_enabled(VirtioBusState *bus);
int virtio_bus_start_ioeventfd(VirtioBusState *bus);
/* Stop the ioeventfd. */
void virtio_bus_stop_ioeventfd(VirtioBusState *bus);
/* Tell the bus that vhost is grabbing the ioeventfd. */
int virtio_bus_grab_ioeventfd(VirtioBusState *bus);
/* bus that vhost is not using the ioeventfd anymore. */
void virtio_bus_release_ioeventfd(VirtioBusState *bus);
/* Switch from/to the generic ioeventfd handler */
int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign);

2
include/hw/virtio/virtio.h
View file

@ -272,6 +272,8 @@ void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
bool with_irqfd);
int virtio_device_start_ioeventfd(VirtIODevice *vdev);
void virtio_device_stop_ioeventfd(VirtIODevice *vdev);
int virtio_device_grab_ioeventfd(VirtIODevice *vdev);
void virtio_device_release_ioeventfd(VirtIODevice *vdev);
bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev);
EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
void virtio_queue_host_notifier_read(EventNotifier *n);