Re: [PATCH v1 1/1] virtio: Restore semantics of vq->broken in virtqueues
From: Alexander Atanasov
Date: Thu Jun 30 2022 - 06:09:02 EST
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