On Tue, May 10, 2022 at 7:32 PM Michael S. Tsirkin <mst@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > Cc: Marc Zyngier <maz@xxxxxxxxxx>
> > Cc: Halil Pasic <pasic@xxxxxxxxxxxxx>
> > Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > 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
>
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