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Re: [Qemu-devel] [PATCH] virtio-serial: add enable_backend callback
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-serial: add enable_backend callback |
Date: |
Fri, 15 Sep 2017 19:09:28 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
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 <address@hidden>
To understand the patch better this doesn't fix _all_ stopped states,
only migration, right? That said it's a valid bugfix even independent
of the effects for stopped runstate.
Thanks,
Paolo
> ---
> 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);
> + }
> +}
> +
> 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;
> k->guest_writable = guest_writable;
> dc->props = virtserialport_properties;
> }
> diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
> index f5bc173844..f0f18c8e7c 100644
> --- a/hw/char/virtio-serial-bus.c
> +++ b/hw/char/virtio-serial-bus.c
> @@ -637,6 +637,13 @@ static void set_status(VirtIODevice *vdev, uint8_t
> status)
> if (!(status & VIRTIO_CONFIG_S_DRIVER_OK)) {
> guest_reset(vser);
> }
> +
> + QTAILQ_FOREACH(port, &vser->ports, next) {
> + VirtIOSerialPortClass *vsc = VIRTIO_SERIAL_PORT_GET_CLASS(port);
> + if (vsc->enable_backend) {
> + vsc->enable_backend(port, vdev->vm_running);
> + }
> + }
> }
>
> static void vser_reset(VirtIODevice *vdev)
> diff --git a/include/hw/virtio/virtio-serial.h
> b/include/hw/virtio/virtio-serial.h
> index b19c44727f..12657a9f39 100644
> --- a/include/hw/virtio/virtio-serial.h
> +++ b/include/hw/virtio/virtio-serial.h
> @@ -58,6 +58,9 @@ typedef struct VirtIOSerialPortClass {
> /* Guest opened/closed device. */
> void (*set_guest_connected)(VirtIOSerialPort *port, int guest_connected);
>
> + /* Enable/disable backend for virtio serial port */
> + void (*enable_backend)(VirtIOSerialPort *port, bool enable);
> +
> /* Guest is now ready to accept data (virtqueues set up). */
> void (*guest_ready)(VirtIOSerialPort *port);
>
>