linux-kernel - Re: [PATCH 2/7] s390/vfio_ap: check TAPQ response code when waiting for queue reset

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Date:   Thu, 15 Dec 2022 11:48:46 +0100
From:   Harald Freudenberger <freude@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, mjrosato@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com
Subject: Re: [PATCH 2/7] s390/vfio_ap: check TAPQ response code when waiting
 for queue reset

On 2022-12-13 16:44, Tony Krowiak wrote:
> The vfio_ap_mdev_reset_queue() function does not check the status
> response code returned form the PQAP(TAPQ) function when verifying the
> queue's status; consequently, there is no way of knowing whether
> verification failed because the wait time was exceeded, or because the
> PQAP(TAPQ) failed.
> 
> This patch adds a function to check the status response code from the
> PQAP(TAPQ) instruction and logs an appropriate message if it fails.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 36 ++++++++++++++++++++++++++-----
>  1 file changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
> b/drivers/s390/crypto/vfio_ap_ops.c
> index 83ff94a38102..a5530a46cf31 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1587,23 +1587,49 @@ static struct vfio_ap_queue
> *vfio_ap_find_queue(int apqn)
>  	return q;
>  }
> 
> +static int apq_status_check(int apqn, struct ap_queue_status *status)
> +{
> +	switch (status->response_code) {
> +	case AP_RESPONSE_NORMAL:
> +	case AP_RESPONSE_RESET_IN_PROGRESS:
> +		if (status->queue_empty && !status->irq_enabled)
> +			return 0;
> +		return -EBUSY;
> +	case AP_RESPONSE_DECONFIGURED:
> +		/*
> +		 * If the AP queue is deconfigured, any subsequent AP command
> +		 * targeting the queue will fail with the same response code. On the
> +		 * other hand, when an AP adapter is deconfigured, the associated
> +		 * queues are reset, so let's return a value indicating the reset
> +		 * for which we're waiting completed successfully.
> +		 */
> +		return 0;
> +	default:
> +		WARN(true,
> +		     "failed to verify reset of queue %02x.%04x: TAPQ rc=%u\n",
> +		     AP_QID_CARD(apqn), AP_QID_QUEUE(apqn),
> +		     status->response_code);
> +		return -EIO;
> +	}
> +}
> +
>  static int apq_reset_check(struct vfio_ap_queue *q)
>  {
> -	int iters = 2;
> +	int iters = 2, ret;
>  	struct ap_queue_status status;
> 
>  	while (iters--) {
>  		msleep(20);
>  		status = ap_tapq(q->apqn, NULL);
> -		if (status.queue_empty && !status.irq_enabled)
> -			return 0;
> +		ret = apq_status_check(q->apqn, &status);
> +		if (ret != -EBUSY)
> +			return ret;
>  	}
>  	WARN_ONCE(iters <= 0,
>  		  "timeout verifying reset of queue %02x.%04x (%u, %u, %u)",
>  		  AP_QID_CARD(q->apqn), AP_QID_QUEUE(q->apqn),
>  		  status.queue_empty, status.irq_enabled, status.response_code);
> -
> -	return -EBUSY;
> +	return ret;
>  }
> 
>  static int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q,

Reviewed-by: Harald Freudenberger <freude@...ux.ibm.com>

Just one word here: this function is only called once and it is very 
very special
to just check the status after RAPQ/ZAPQ. I would merge this function 
into the
calling code or rename the function to reflect the special condition 
under which
it is called. However - this is not my code and I don't need to maintain 
it, so
maybe simple ignore my words.