[Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Stefan Hajnoczi]

When the dataplane thread stops, its vring.c implementation synchronizes
vring state back to virtio.c so we can continue emulating the virtio
device.

This patch ensures that virtio.c's signalled_used_valid flag is reset so
that we do not suppress guest notifications due to stale signalled_used
values.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/virtio/dataplane/vring.c | 1 +
 hw/virtio/virtio.c          | 5 +++++
 include/hw/virtio/virtio.h  | 1 +
 3 files changed, 7 insertions(+)

diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c
index 82cc151..351a343 100644
--- a/hw/virtio/dataplane/vring.c
+++ b/hw/virtio/dataplane/vring.c
@@ -52,6 +52,7 @@ bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
 void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
 {
     virtio_queue_set_last_avail_idx(vdev, n, vring->last_avail_idx);
+    virtio_queue_invalidate_signalled_used(vdev, n);
 
     hostmem_finalize(&vring->hostmem);
 }
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 09f62c6..706bdf4 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -1059,6 +1059,11 @@ void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
     vdev->vq[n].last_avail_idx = idx;
 }
 
+void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n)
+{
+    vdev->vq[n].signalled_used_valid = false;
+}
+
 VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n)
 {
     return vdev->vq + n;
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index d7e9e0f..a90522d 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -237,6 +237,7 @@ hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n);
 hwaddr virtio_queue_get_ring_size(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
 void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
+void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n);
 VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
 uint16_t virtio_get_queue_index(VirtQueue *vq);
 int virtio_queue_get_id(VirtQueue *vq);
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Michael S. Tsirkin]

On Mon, Aug 12, 2013 at 11:08:09AM +0200, Stefan Hajnoczi wrote:
> When the dataplane thread stops, its vring.c implementation synchronizes
> vring state back to virtio.c so we can continue emulating the virtio
> device.
> 
> This patch ensures that virtio.c's signalled_used_valid flag is reset so
> that we do not suppress guest notifications due to stale signalled_used
> values.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Good point

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

and we also need this for vhost.c right?

> ---
>  hw/virtio/dataplane/vring.c | 1 +
>  hw/virtio/virtio.c          | 5 +++++
>  include/hw/virtio/virtio.h  | 1 +
>  3 files changed, 7 insertions(+)
> 
> diff --git a/hw/virtio/dataplane/vring.c b/hw/virtio/dataplane/vring.c
> index 82cc151..351a343 100644
> --- a/hw/virtio/dataplane/vring.c
> +++ b/hw/virtio/dataplane/vring.c
> @@ -52,6 +52,7 @@ bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
>  void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
>  {
>      virtio_queue_set_last_avail_idx(vdev, n, vring->last_avail_idx);
> +    virtio_queue_invalidate_signalled_used(vdev, n);
>  
>      hostmem_finalize(&vring->hostmem);
>  }
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 09f62c6..706bdf4 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1059,6 +1059,11 @@ void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx)
>      vdev->vq[n].last_avail_idx = idx;
>  }
>  
> +void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n)
> +{
> +    vdev->vq[n].signalled_used_valid = false;
> +}
> +
>  VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n)
>  {
>      return vdev->vq + n;
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index d7e9e0f..a90522d 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -237,6 +237,7 @@ hwaddr virtio_queue_get_used_size(VirtIODevice *vdev, int n);
>  hwaddr virtio_queue_get_ring_size(VirtIODevice *vdev, int n);
>  uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
>  void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
> +void virtio_queue_invalidate_signalled_used(VirtIODevice *vdev, int n);
>  VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
>  uint16_t virtio_get_queue_index(VirtQueue *vq);
>  int virtio_queue_get_id(VirtQueue *vq);
> -- 
> 1.8.3.1

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Kevin Wolf]

Am 12.08.2013 um 11:08 hat Stefan Hajnoczi geschrieben:
> When the dataplane thread stops, its vring.c implementation synchronizes
> vring state back to virtio.c so we can continue emulating the virtio
> device.
> 
> This patch ensures that virtio.c's signalled_used_valid flag is reset so
> that we do not suppress guest notifications due to stale signalled_used
> values.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Stefan Hajnoczi]

On Mon, Aug 12, 2013 at 11:18 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Mon, Aug 12, 2013 at 11:08:09AM +0200, Stefan Hajnoczi wrote:
>> When the dataplane thread stops, its vring.c implementation synchronizes
>> vring state back to virtio.c so we can continue emulating the virtio
>> device.
>>
>> This patch ensures that virtio.c's signalled_used_valid flag is reset so
>> that we do not suppress guest notifications due to stale signalled_used
>> values.
>>
>> Suggested-by: Kevin Wolf <kwolf@redhat.com>
>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>
> Good point
>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>
> and we also need this for vhost.c right?

I think vhost is not affected by this because virtio.c clears the
signalled_used_valid flag when the device is reset.  Since vhost_net
does not transition back and forth between userspace virtio and vhost
(without a device reset), there is no need to reset the flag.

Stefan

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Michael S. Tsirkin]

On Mon, Aug 12, 2013 at 03:39:23PM +0200, Stefan Hajnoczi wrote:
> On Mon, Aug 12, 2013 at 11:18 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Mon, Aug 12, 2013 at 11:08:09AM +0200, Stefan Hajnoczi wrote:
> >> When the dataplane thread stops, its vring.c implementation synchronizes
> >> vring state back to virtio.c so we can continue emulating the virtio
> >> device.
> >>
> >> This patch ensures that virtio.c's signalled_used_valid flag is reset so
> >> that we do not suppress guest notifications due to stale signalled_used
> >> values.
> >>
> >> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> >> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> >
> > Good point
> >
> > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> >
> > and we also need this for vhost.c right?
> 
> I think vhost is not affected by this because virtio.c clears the
> signalled_used_valid flag when the device is reset.  Since vhost_net
> does not transition back and forth between userspace virtio and vhost
> (without a device reset), there is no need to reset the flag.
> 
> Stefan

Yes it does transition on vm stop/start.

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Stefan Hajnoczi]

On Mon, Aug 12, 2013 at 05:10:11PM +0300, Michael S. Tsirkin wrote:
> On Mon, Aug 12, 2013 at 03:39:23PM +0200, Stefan Hajnoczi wrote:
> > On Mon, Aug 12, 2013 at 11:18 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > > On Mon, Aug 12, 2013 at 11:08:09AM +0200, Stefan Hajnoczi wrote:
> > >> When the dataplane thread stops, its vring.c implementation synchronizes
> > >> vring state back to virtio.c so we can continue emulating the virtio
> > >> device.
> > >>
> > >> This patch ensures that virtio.c's signalled_used_valid flag is reset so
> > >> that we do not suppress guest notifications due to stale signalled_used
> > >> values.
> > >>
> > >> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> > >> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > >
> > > Good point
> > >
> > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > >
> > > and we also need this for vhost.c right?
> > 
> > I think vhost is not affected by this because virtio.c clears the
> > signalled_used_valid flag when the device is reset.  Since vhost_net
> > does not transition back and forth between userspace virtio and vhost
> > (without a device reset), there is no need to reset the flag.
> > 
> > Stefan
> 
> Yes it does transition on vm stop/start.

I see.  Come to think of it maybe dataplane could use virtio.c's vm
change state handler instead of registering its own.  Anyway, thanks for
pointing this out.

Stefan

Re: [Qemu-devel] [PATCH for-1.6] virtio: clear signalled_used_valid when switching from dataplane

[Michael S. Tsirkin]

On Tue, Aug 13, 2013 at 10:14:11AM +0200, Stefan Hajnoczi wrote:
> On Mon, Aug 12, 2013 at 05:10:11PM +0300, Michael S. Tsirkin wrote:
> > On Mon, Aug 12, 2013 at 03:39:23PM +0200, Stefan Hajnoczi wrote:
> > > On Mon, Aug 12, 2013 at 11:18 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > > > On Mon, Aug 12, 2013 at 11:08:09AM +0200, Stefan Hajnoczi wrote:
> > > >> When the dataplane thread stops, its vring.c implementation synchronizes
> > > >> vring state back to virtio.c so we can continue emulating the virtio
> > > >> device.
> > > >>
> > > >> This patch ensures that virtio.c's signalled_used_valid flag is reset so
> > > >> that we do not suppress guest notifications due to stale signalled_used
> > > >> values.
> > > >>
> > > >> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> > > >> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > >
> > > > Good point
> > > >
> > > > Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> > > >
> > > > and we also need this for vhost.c right?
> > > 
> > > I think vhost is not affected by this because virtio.c clears the
> > > signalled_used_valid flag when the device is reset.  Since vhost_net
> > > does not transition back and forth between userspace virtio and vhost
> > > (without a device reset), there is no need to reset the flag.
> > > 
> > > Stefan
> > 
> > Yes it does transition on vm stop/start.
> 
> I see.  Come to think of it maybe dataplane could use virtio.c's vm
> change state handler instead of registering its own.  Anyway, thanks for
> pointing this out.
> 
> Stefan

It probably should esp if you have a handler for virtio status:
this is the only way to guarantee they are called in a sane order.

-- 
MST