On 07/07/2017 16:21, Pavel Butsykin wrote:
> We should guarantee that RAM will not be modified while VM has a stopped
> state, otherwise it can lead to negative consequences during post-copy
> migration. In RUN_STATE_FINISH_MIGRATE step, it's expected that RAM on
> source side will not be modified as this could lead to non-consistent vm state
> on the destination side. Also RAM access during postcopy-ram migration with
> enabled release-ram capability can lead to sad consequences.
>
> Let's add enable_backend() callback to avoid undesirable virtioqueue changes
> in the guest memory.
>
> Signed-off-by: Pavel Butsykin <pbutsy...@virtuozzo.com>
> ---
> hw/char/virtio-console.c | 21 +++++++++++++++++++++
> hw/char/virtio-serial-bus.c | 7 +++++++
> include/hw/virtio/virtio-serial.h | 3 +++
> 3 files changed, 31 insertions(+)
>
> diff --git a/hw/char/virtio-console.c b/hw/char/virtio-console.c
> index 0cb1668c8a..b55905892e 100644
> --- a/hw/char/virtio-console.c
> +++ b/hw/char/virtio-console.c
> @@ -163,6 +163,26 @@ static void chr_event(void *opaque, int event)
> }
> }
>
> +static void virtconsole_enable_backend(VirtIOSerialPort *port, bool enable)
> +{
> + VirtConsole *vcon = VIRTIO_CONSOLE(port);
> +
> + if (!qemu_chr_fe_get_driver(&vcon->chr)) {
> + return;
> + }
> +
> + if (enable) {
> + VirtIOSerialPortClass *k = VIRTIO_SERIAL_PORT_GET_CLASS(port);
> +
> + qemu_chr_fe_set_handlers(&vcon->chr, chr_can_read, chr_read,
> + k->is_console ? NULL : chr_event,
> + vcon, NULL, false);
> + } else {
> + qemu_chr_fe_set_handlers(&vcon->chr, NULL, NULL,
> + NULL, NULL, NULL, false);
> + }
> +}
I think you can also factorize the code in virtconsole_realize() to call
this new function.
> static void virtconsole_realize(DeviceState *dev, Error **errp)
> {
> VirtIOSerialPort *port = VIRTIO_SERIAL_PORT(dev);
> @@ -233,6 +253,7 @@ static void virtserialport_class_init(ObjectClass *klass,
> void *data)
> k->unrealize = virtconsole_unrealize;
> k->have_data = flush_buf;
> k->set_guest_connected = set_guest_connected;
> + k->enable_backend = virtconsole_enable_backend;
Why don't you register a vm_state change handler to change the state of
the virtconsole according to the state of the machine instead of adding
a new function in the VirtIOSerialPortClass?
See a23a6d1 ("virtio-rng: stop virtqueue while the CPU is stopped")
Thanks,
Laurent
