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X-Received-From: 2607:f8b0:4864:20::742 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 , Zhang Yu , "Michael S. Tsirkin" , qemu-devel , "Dr. David Alan Gilbert" , Xie Yongji , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 29 May 2019 at 21:02, Greg Kurz wrote: > > On Wed, 29 May 2019 13:38:19 +0100 > "Dr. David Alan Gilbert" wrote: > > > * Greg Kurz (groug@kaod.org) wrote: > > > On Wed, 29 May 2019 12:18:50 +0100 > > > "Dr. David Alan Gilbert" wrote: > > > > > > > * Greg Kurz (groug@kaod.org) wrote: > > > > > On Tue, 28 May 2019 10:08:54 +1000 > > > > > David Gibson wrote: > > > > > > > > > > > On Fri, May 24, 2019 at 12:19:09PM +0200, 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. > > > > > > > > > > > > > > Cc'ing David for his opinion. > > > > > > > > > > > > Uh.. did you mean to CC me, or Dave Gilbert? > > > > > > > > > > > > > > > > Oops... Dave Gilbert indeed, but you're thoughts on that matter are valuable > > > > > as well. I remember being involved in backward migration fixes for spapr > > > > > several times. > > > > > > > > > > > I mean, I think you're right that we should try to maintain backwards > > > > > > migration, but this isn't really my area of authority. > > > > > > > > > > > > > > > > Cc'ing Dave Gilbert :) > > > > > > > > Right, I need to maintain backwards migration compatibility; tie the > > > > feature to a machine type so it's only used on newer machine types and > > > > then we'll be safe. > > > > > > > > Having said that, what's the symptom when this goes wrong? > > > > > > > > > > Since the started flag is set as soon as the guest driver begins to use > > > the device and remains so until next reset, the associated subsection is > > > basically always emitted when migrating a booted guest. This causes > > > migration to always fail on the target in this case: > > > > I meant what's the symptom without this patch series at all? > > > > Oh sorry... if I got it right, migrating when the guest first kicked the > device but not set the DRIVE_OK bit yet would result in a guest hang on > the destination. Yongji might elaborate a bit more on that. > Yes, that's the issue that my patch tries to fix. It only happens in a short window for virtio 1.0 transitional devices. Thanks, Yongji