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Date:   Thu, 30 Jun 2022 13:08:53 +0300
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Subject: Re: [PATCH v1 1/1] virtio: Restore semantics of vq->broken in
 virtqueues
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To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Jason Wang <jasowang@redhat.com>, kernel@openvz.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Marc Zyngier <maz@kernel.org>,
        Halil Pasic <pasic@linux.ibm.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Vineeth Vijayan <vneethv@linux.ibm.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>,
        linux-s390@vger.kernel.org, Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
References: <20220630093651.25981-1-alexander.atanasov@virtuozzo.com>
 <20220630054532-mutt-send-email-mst@kernel.org>
From:   Alexander Atanasov <alexander.atanasov@virtuozzo.com>
In-Reply-To: <20220630054532-mutt-send-email-mst@kernel.org>
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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@virtuozzo.com>
>
> Does
>
> commit c346dae4f3fbce51bbd4f2ec5e8c6f9b91e93163
> Author: Jason Wang <jasowang@redhat.com>
> 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@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>
>> Cc: Vineeth Vijayan <vneethv@linux.ibm.com>
>> Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
>> Cc: linux-s390@vger.kernel.org
>> Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>>
>>
>> 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