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Tsirkin" , David Gibson Content-Type: text/plain; charset="UTF-8" X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::741 Subject: Re: [Qemu-devel] [PULL v2 04/36] virtio: Introduce started flag to VirtioDevice X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Xie Yongji , qemu-devel , Zhang Yu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 24 May 2019 at 18:20, Greg Kurz wrote: > > On Mon, 20 May 2019 19:10:35 -0400 > "Michael S. Tsirkin" wrote: > > > From: Xie Yongji > > > > 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 > > Signed-off-by: Zhang Yu > > Message-Id: <20190320112646.3712-2-xieyongji@baidu.com> > > Reviewed-by: Michael S. Tsirkin > > Signed-off-by: Michael S. Tsirkin > > --- > > 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. Not sure if there is a more general approach... Thanks, Yongji