Re: [PATCH V4 8/9] virtio: harden vring IRQ

[Jason Wang <jasowang@redhat.com>]

On Tue, May 10, 2022 at 7:32 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Sat, May 07, 2022 at 03:19:53PM +0800, Jason Wang wrote:
> > This is a rework on the previous IRQ hardening that is done for
> > virtio-pci where several drawbacks were found and were reverted:
> >
> > 1) try to use IRQF_NO_AUTOEN which is not friendly to affinity managed IRQ
> >    that is used by some device such as virtio-blk
> > 2) done only for PCI transport
> >
> > The vq->broken is re-used in this patch for implementing the IRQ
> > hardening. The vq->broken is set to true during both initialization
> > and reset. And the vq->broken is set to false in
> > virtio_device_ready(). Then vring_interrupt can check and return when
> > vq->broken is true. And in this case, switch to return IRQ_NONE to let
> > the interrupt core aware of such invalid interrupt to prevent IRQ
> > storm.
> >
> > The reason of using a per queue variable instead of a per device one
> > is that we may need it for per queue reset hardening in the future.
> >
> > Note that the hardening is only done for vring interrupt since the
> > config interrupt hardening is already done in commit 22b7050a024d7
> > ("virtio: defer config changed notifications"). But the method that is
> > used by config interrupt can't be reused by the vring interrupt
> > handler because it uses spinlock to do the synchronization which is
> > expensive.
> >
> > 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>
> > ---
> >  drivers/virtio/virtio.c       | 15 ++++++++++++---
> >  drivers/virtio/virtio_ring.c  | 11 +++++++----
> >  include/linux/virtio_config.h | 12 ++++++++++++
> >  3 files changed, 31 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > index 8dde44ea044a..696f5ba4f38e 100644
> > --- a/drivers/virtio/virtio.c
> > +++ b/drivers/virtio/virtio.c
> > @@ -220,6 +220,15 @@ static int virtio_features_ok(struct virtio_device *dev)
> >   * */
> >  void virtio_reset_device(struct virtio_device *dev)
> >  {
> > +     /*
> > +      * The below virtio_synchronize_cbs() guarantees that any
> > +      * interrupt for this line arriving after
> > +      * virtio_synchronize_vqs() has completed is guaranteed to see
> > +      * driver_ready == false.
> > +      */
> > +     virtio_break_device(dev);
> > +     virtio_synchronize_cbs(dev);
> > +
> >       dev->config->reset(dev);
> >  }
> >  EXPORT_SYMBOL_GPL(virtio_reset_device);
> > @@ -428,6 +437,9 @@ int register_virtio_device(struct virtio_device *dev)
> >       dev->config_enabled = false;
> >       dev->config_change_pending = false;
> >
> > +     INIT_LIST_HEAD(&dev->vqs);
> > +     spin_lock_init(&dev->vqs_list_lock);
> > +
> >       /* We always start by resetting the device, in case a previous
> >        * driver messed it up.  This also tests that code path a little. */
> >       virtio_reset_device(dev);
> > @@ -435,9 +447,6 @@ int register_virtio_device(struct virtio_device *dev)
> >       /* Acknowledge that we've seen the device. */
> >       virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
> >
> > -     INIT_LIST_HEAD(&dev->vqs);
> > -     spin_lock_init(&dev->vqs_list_lock);
> > -
> >       /*
> >        * device_add() causes the bus infrastructure to look for a matching
> >        * driver.
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 5b7df7c455f0..9dfad2890d7a 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -1690,7 +1690,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
> >       vq->we_own_ring = true;
> >       vq->notify = notify;
> >       vq->weak_barriers = weak_barriers;
> > -     vq->broken = false;
> > +     vq->broken = true;
> >       vq->last_used_idx = 0;
> >       vq->event_triggered = false;
> >       vq->num_added = 0;
> > @@ -2136,8 +2136,11 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
> >               return IRQ_NONE;
> >       }
> >
> > -     if (unlikely(vq->broken))
> > -             return IRQ_HANDLED;
> > +     if (unlikely(vq->broken)) {
> > +             dev_warn_once(&vq->vq.vdev->dev,
> > +                           "virtio vring IRQ raised before DRIVER_OK");
> > +             return IRQ_NONE;
> > +     }
> >
> >       /* Just a hint for performance: so it's ok that this can be racy! */
> >       if (vq->event)
> > @@ -2179,7 +2182,7 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >       vq->we_own_ring = false;
> >       vq->notify = notify;
> >       vq->weak_barriers = weak_barriers;
> > -     vq->broken = false;
> > +     vq->broken = true;
> >       vq->last_used_idx = 0;
> >       vq->event_triggered = false;
> >       vq->num_added = 0;
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index d8a2340f928e..23f1694cdbd5 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -256,6 +256,18 @@ void virtio_device_ready(struct virtio_device *dev)
> >       unsigned status = dev->config->get_status(dev);
> >
> >       BUG_ON(status & VIRTIO_CONFIG_S_DRIVER_OK);
> > +
> > +     /*
> > +      * The virtio_synchronize_cbs() makes sure vring_interrupt()
> > +      * will see the driver specific setup if it sees vq->broken
> > +      * as false.
> > +      */
> > +     virtio_synchronize_cbs(dev);
>
> since you mention vq->broken above, maybe add
>         "set vq->broken to false"

Ok.

>
> > +     __virtio_unbreak_device(dev);
> > +     /*
> > +      * The transport is expected ensure the visibility of
>
> to ensure

Will fix.

>
> > +      * vq->broken
>
> let's add: "visibility by vq callbacks"

Sure.

>
> > before setting VIRTIO_CONFIG_S_DRIVER_OK.
> > +      */
>
>
> Can I see some analysis of existing transports showing
> this is actually the case for them?

Yes.

> And maybe add a comment near set_status to document the
> requirement.

For PCI and MMIO, we can quote the memory-barriers.txt or explain that
wmb() is not needed before the MMIO writel().
For CCW, it looks not obvious, it looks to me the IO was submitted via
__ssch() which has an inline assembly.  Cornelia and Hali, could you
help me to understand if and how did virtio_ccw_set_status() can
ensure the visibility of the previous driver setup and vq->broken
here?

Thanks

>
> >       dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> >  }
> >
> > --
> > 2.25.1
>