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Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to Virti
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice |
Date: |
Mon, 27 May 2019 14:53:57 -0400 |
On Mon, May 27, 2019 at 12:44:46PM +0200, Greg Kurz wrote:
> On Fri, 24 May 2019 19:56:06 +0800
> Yongji Xie <address@hidden> wrote:
>
> > On Fri, 24 May 2019 at 18:20, Greg Kurz <address@hidden> wrote:
> > >
> > > On Mon, 20 May 2019 19:10:35 -0400
> > > "Michael S. Tsirkin" <address@hidden> wrote:
> > >
> > > > From: Xie Yongji <address@hidden>
> > > >
> > > > The virtio 1.0 transitional devices support driver uses the device
> > > > before setting the DRIVER_OK status bit. So we introduce a started
> > > > flag to indicate whether driver has started the device or not.
> > > >
> > > > Signed-off-by: Xie Yongji <address@hidden>
> > > > Signed-off-by: Zhang Yu <address@hidden>
> > > > Message-Id: <address@hidden>
> > > > Reviewed-by: Michael S. Tsirkin <address@hidden>
> > > > Signed-off-by: Michael S. Tsirkin <address@hidden>
> > > > ---
> > > > include/hw/virtio/virtio.h | 2 ++
> > > > hw/virtio/virtio.c | 52 ++++++++++++++++++++++++++++++++++++--
> > > > 2 files changed, 52 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > > > index 7140381e3a..27c0efc3d0 100644
> > > > --- a/include/hw/virtio/virtio.h
> > > > +++ b/include/hw/virtio/virtio.h
> > > > @@ -105,6 +105,8 @@ struct VirtIODevice
> > > > uint16_t device_id;
> > > > bool vm_running;
> > > > bool broken; /* device in invalid state, needs reset */
> > > > + bool started;
> > > > + bool start_on_kick; /* virtio 1.0 transitional devices support
> > > > that */
> > > > VMChangeStateEntry *vmstate;
> > > > char *bus_name;
> > > > uint8_t device_endian;
> > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > > index 28056a7ef7..5d533ac74e 100644
> > > > --- a/hw/virtio/virtio.c
> > > > +++ b/hw/virtio/virtio.c
> > > > @@ -1162,10 +1162,16 @@ int virtio_set_status(VirtIODevice *vdev,
> > > > uint8_t val)
> > > > }
> > > > }
> > > > }
> > > > + vdev->started = val & VIRTIO_CONFIG_S_DRIVER_OK;
> > > > + if (unlikely(vdev->start_on_kick && vdev->started)) {
> > > > + vdev->start_on_kick = false;
> > > > + }
> > > > +
> > > > if (k->set_status) {
> > > > k->set_status(vdev, val);
> > > > }
> > > > vdev->status = val;
> > > > +
> > > > return 0;
> > > > }
> > > >
> > > > @@ -1208,6 +1214,9 @@ void virtio_reset(void *opaque)
> > > > k->reset(vdev);
> > > > }
> > > >
> > > > + vdev->start_on_kick = (virtio_host_has_feature(vdev,
> > > > VIRTIO_F_VERSION_1) &&
> > > > + !virtio_vdev_has_feature(vdev,
> > > > VIRTIO_F_VERSION_1));
> > > > + vdev->started = false;
> > > > vdev->broken = false;
> > > > vdev->guest_features = 0;
> > > > vdev->queue_sel = 0;
> > > > @@ -1518,14 +1527,21 @@ void virtio_queue_set_align(VirtIODevice *vdev,
> > > > int n, int align)
> > > >
> > > > static bool virtio_queue_notify_aio_vq(VirtQueue *vq)
> > > > {
> > > > + bool ret = false;
> > > > +
> > > > if (vq->vring.desc && vq->handle_aio_output) {
> > > > VirtIODevice *vdev = vq->vdev;
> > > >
> > > > trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
> > > > - return vq->handle_aio_output(vdev, vq);
> > > > + ret = vq->handle_aio_output(vdev, vq);
> > > > +
> > > > + if (unlikely(vdev->start_on_kick)) {
> > > > + vdev->started = true;
> > > > + vdev->start_on_kick = false;
> > > > + }
> > > > }
> > > >
> > > > - return false;
> > > > + return ret;
> > > > }
> > > >
> > > > static void virtio_queue_notify_vq(VirtQueue *vq)
> > > > @@ -1539,6 +1555,11 @@ static void virtio_queue_notify_vq(VirtQueue *vq)
> > > >
> > > > trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
> > > > vq->handle_output(vdev, vq);
> > > > +
> > > > + if (unlikely(vdev->start_on_kick)) {
> > > > + vdev->started = true;
> > > > + vdev->start_on_kick = false;
> > > > + }
> > > > }
> > > > }
> > > >
> > > > @@ -1556,6 +1577,11 @@ void virtio_queue_notify(VirtIODevice *vdev, int
> > > > n)
> > > > } else if (vq->handle_output) {
> > > > vq->handle_output(vdev, vq);
> > > > }
> > > > +
> > > > + if (unlikely(vdev->start_on_kick)) {
> > > > + vdev->started = true;
> > > > + vdev->start_on_kick = false;
> > > > + }
> > > > }
> > > >
> > > > uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)
> > > > @@ -1770,6 +1796,13 @@ static bool virtio_broken_needed(void *opaque)
> > > > return vdev->broken;
> > > > }
> > > >
> > > > +static bool virtio_started_needed(void *opaque)
> > > > +{
> > > > + VirtIODevice *vdev = opaque;
> > > > +
> > > > + return vdev->started;
> > >
> > > Existing machine types don't know about the "virtio/started" subsection.
> > > This
> > > breaks migration to older QEMUs if the driver has started the device, ie.
> > > most
> > > probably always when it comes to live migration.
> > >
> > > My understanding is that we do try to support backward migration though.
> > > It
> > > is a regular practice in datacenters to migrate workloads without having
> > > to
> > > take care of the QEMU version. FWIW I had to fix similar issues downstream
> > > many times in the past because customers had filed bugs.
> > >
> >
> > If we do need to support backward migration, for this patch, what I
> > can think of is to only migrate the flag in the case that guest kicks
> > but not set DRIVER_OK. This could fix backward migration in most case.
>
> You mean something like that ?
>
> static bool virtio_started_needed(void *opaque)
> {
> VirtIODevice *vdev = opaque;
>
> return vdev->started && !(vdev->status & VIRTIO_CONFIG_S_DRIVER_OK);
> }
>
> > Not sure if there is a more general approach...
> >
>
> Another approach would be to only implement the started flag for
> machine version > 4.0. This can be achieved by adding a "use-started"
> property to the base virtio device, true by default and set to
> false by hw_compat_4_0.
I think this is best frankly.
> > Thanks,
> > Yongji
- Re: [Qemu-devel] [PATCH v2 1/2] hw: report invalid disable-legacy|modern usage for virtio-1-only devs, (continued)
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, David Gibson, 2019/05/27
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Greg Kurz, 2019/05/28
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Dr. David Alan Gilbert, 2019/05/29
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Greg Kurz, 2019/05/29
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Dr. David Alan Gilbert, 2019/05/29
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Greg Kurz, 2019/05/29
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Dr. David Alan Gilbert, 2019/05/29
- Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice, Yongji Xie, 2019/05/29