Re: [PATCH V3 3/9] virtio: introduce config op to synchronize vring callbacks

Jason Wang
2022-04-29T02:09:00Z

On Thu, Apr 28, 2022 at 5:13 PM Cornelia Huck <cohuck@redhat.com> wrote:
>
> On Mon, Apr 25 2022, Jason Wang <jasowang@redhat.com> wrote:
>
> > This patch introduces new virtio config op to vring
> > callbacks. Transport specific method is required to make sure the
> > write before this function is visible to the vring_interrupt() that is
>
> Which kind of writes? I.e., what is the scope?

Any writes before synchronize_cbs(). Is something like the following better?

The function guarantees that all memory operations before it are
visible to the vring_interrupt() that is called after it.

>
> > called after the return of this function. For the transport that
> > doesn't provide synchronize_vqs(), use synchornize_rcu() which
>
> Typo: synchronize_rcu()

Will fix it.

Thanks

>
> > synchronize with IRQ implicitly as a fallback.
> >
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: "Paul E. McKenney" <paulmck@kernel.org>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Halil Pasic <pasic@linux.ibm.com>
> > Cc: Cornelia Huck <cohuck@redhat.com>
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > ---
> > include/linux/virtio_config.h | 24 ++++++++++++++++++++++++
> > 1 file changed, 24 insertions(+)
> >
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index b341dd62aa4d..14fe89ff99c7 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -57,6 +57,10 @@ struct virtio_shm_region {
> > * include a NULL entry for vqs unused by driver
> > * Returns 0 on success or error status
> > * @del_vqs: free virtqueues found by find_vqs().
> > + * @synchronize_cbs: synchronize with the virtqueue callbacks (optional)
> > + * Make sure the writes commited before this method is visible to
> > + * vring_interrupt() which is called after this method.
>
> Same here, I think the description needs to be a bit more explicit about
> which writes we care about here.
>
> > + * vdev: the virtio_device
> > * @get_features: get the array of feature bits for this device.
> > * vdev: the virtio_device
> > * Returns the first 64 feature bits (all we currently need).
> > @@ -89,6 +93,7 @@ struct virtio_config_ops {
> > const char * const names[], const bool *ctx,
> > struct irq_affinity *desc);
> > void (*del_vqs)(struct virtio_device *);
> > + void (*synchronize_cbs)(struct virtio_device *);
> > u64 (*get_features)(struct virtio_device *vdev);
> > int (*finalize_features)(struct virtio_device *vdev);
> > const char *(*bus_name)(struct virtio_device *vdev);
>