Re: [PATCH v1 1/1] virtio: Restore semantics of vq->broken in virtqueues

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Hello,

On 30/06/2022 12:46, Michael S. Tsirkin wrote:
On Thu, Jun 30, 2022 at 09:36:46AM +0000, Alexander Atanasov wrote:
virtio: harden vring IRQ (8b4ec69d7e09) changed the use
of vq->broken. As result vring_interrupt handles IRQs for
broken drivers as IRQ_NONE and not IRQ_HANDLED and made impossible
to initiallize vqs before the driver is ready, i.e. in probe method.
Balloon driver does this and it can not load because it fails in
vqs_init with -EIO.

So instead of changing the original intent ot the flag introduce
a new flag vq->ready which servers the purpose to check of early IRQs
and restore the behaviour of the vq->broken flag.

Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx>

Does

commit c346dae4f3fbce51bbd4f2ec5e8c6f9b91e93163
Author: Jason Wang <jasowang@xxxxxxxxxx>
Date:   Wed Jun 22 09:29:40 2022 +0800

     virtio: disable notification hardening by default


solve the problem for you?


No, it won't if CONFIG_VIRTIO_HARDEN_NOTIFICATION is enabled - balloon still won't be able to init vqs.

The problem is in virtqueue_add_split and virtqueue_add_packed - can not set driver_ok without queues.

The return value of the vring_interrupt gets different - and iirc IRQ_NONE for broken device can lead to interrupt storms - i am not sure if that is valid for virtio devices yet but for real harware most likely. Either way if you have a mix of  drivers working differently depending on return of the handler  it would get really messy.

RR's original intent was to flag a driver as bad why reuse it like that  ?


  drivers/virtio/virtio_ring.c  | 20 ++++++++++++++------
  include/linux/virtio.h        |  2 +-
  include/linux/virtio_config.h | 10 +++++-----
  3 files changed, 20 insertions(+), 12 deletions(-)

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>
Cc: Vineeth Vijayan <vneethv@xxxxxxxxxxxxx>
Cc: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
Cc: linux-s390@xxxxxxxxxxxxxxx
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>


diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 13a7348cedff..dca3cc774584 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -100,6 +100,9 @@ struct vring_virtqueue {
  	/* Other side has made a mess, don't try any more. */
  	bool broken;
+ /* the queue is ready to handle interrupts */
+	bool ready;
+
  	/* Host supports indirect buffers */
  	bool indirect;
@@ -1688,7 +1691,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
  	vq->we_own_ring = true;
  	vq->notify = notify;
  	vq->weak_barriers = weak_barriers;
-	vq->broken = true;
+	vq->broken = false;
+	vq->ready = false;
  	vq->last_used_idx = 0;
  	vq->event_triggered = false;
  	vq->num_added = 0;
@@ -2134,7 +2138,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
  		return IRQ_NONE;
  	}
- if (unlikely(vq->broken)) {
+	if (unlikely(vq->broken))
+		return IRQ_HANDLED;
+
+	if (unlikely(!vq->ready)) {
  		dev_warn_once(&vq->vq.vdev->dev,
  			      "virtio vring IRQ raised before DRIVER_OK");
  		return IRQ_NONE;
@@ -2180,7 +2187,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
  	vq->we_own_ring = false;
  	vq->notify = notify;
  	vq->weak_barriers = weak_barriers;
-	vq->broken = true;
+	vq->broken = false;
+	vq->ready = false;
  	vq->last_used_idx = 0;
  	vq->event_triggered = false;
  	vq->num_added = 0;
@@ -2405,7 +2413,7 @@ EXPORT_SYMBOL_GPL(virtio_break_device);
   * (probing and restoring). This function should only be called by the
   * core, not directly by the driver.
   */
-void __virtio_unbreak_device(struct virtio_device *dev)
+void __virtio_device_ready(struct virtio_device *dev)
  {
  	struct virtqueue *_vq;
@@ -2414,11 +2422,11 @@ void __virtio_unbreak_device(struct virtio_device *dev)
  		struct vring_virtqueue *vq = to_vvq(_vq);
/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
-		WRITE_ONCE(vq->broken, false);
+		WRITE_ONCE(vq->ready, true);
  	}
  	spin_unlock(&dev->vqs_list_lock);
  }
-EXPORT_SYMBOL_GPL(__virtio_unbreak_device);
+EXPORT_SYMBOL_GPL(__virtio_device_ready);
dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
  {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d8fdf170637c..538c5959949a 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -131,7 +131,7 @@ void unregister_virtio_device(struct virtio_device *dev);
  bool is_virtio_device(struct device *dev);
void virtio_break_device(struct virtio_device *dev);
-void __virtio_unbreak_device(struct virtio_device *dev);
+void __virtio_device_ready(struct virtio_device *dev);
void virtio_config_changed(struct virtio_device *dev);
  #ifdef CONFIG_PM_SLEEP
diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 49c7c32815f1..35cf1b26e05a 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -259,21 +259,21 @@ void virtio_device_ready(struct virtio_device *dev)
/*
  	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
-	 * will see the driver specific setup if it sees vq->broken
+	 * will see the driver specific setup if it sees vq->ready
  	 * as false (even if the notifications come before DRIVER_OK).
  	 */
  	virtio_synchronize_cbs(dev);
-	__virtio_unbreak_device(dev);
+	__virtio_device_ready(dev);
  	/*
-	 * The transport should ensure the visibility of vq->broken
+	 * The transport should ensure the visibility of vq->ready
  	 * before setting DRIVER_OK. See the comments for the transport
  	 * specific set_status() method.
  	 *
  	 * A well behaved device will only notify a virtqueue after
  	 * DRIVER_OK, this means the device should "see" the coherenct
-	 * memory write that set vq->broken as false which is done by
+	 * memory write that set vq->ready as true which is done by
  	 * the driver when it sees DRIVER_OK, then the following
-	 * driver's vring_interrupt() will see vq->broken as false so
+	 * driver's vring_interrupt() will see vq->true as true so
  	 * we won't lose any notification.
  	 */
  	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
--
2.25.1

--
Regards,
Alexander Atanasov




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