linux-kernel - Re: [PATCH 1/7] s390/vfio-ap: verify reset complete in separate function

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Date:   Thu, 15 Dec 2022 09:24:15 +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 1/7] s390/vfio-ap: verify reset complete in separate
 function

On 2022-12-13 16:44, Tony Krowiak wrote:
> The vfio_ap_mdev_reset_queue() function contains a loop to verify that 
> the
> reset successfully completes within 40ms. This patch moves that loop 
> into
> a separate function.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
> b/drivers/s390/crypto/vfio_ap_ops.c
> index 0b4cc8c597ae..83ff94a38102 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1587,12 +1587,30 @@ static struct vfio_ap_queue
> *vfio_ap_find_queue(int apqn)
>  	return q;
>  }
> 
> +static int apq_reset_check(struct vfio_ap_queue *q)
> +{
> +	int iters = 2;
> +	struct ap_queue_status status;
> +
> +	while (iters--) {
> +		msleep(20);
> +		status = ap_tapq(q->apqn, NULL);
> +		if (status.queue_empty && !status.irq_enabled)
> +			return 0;
> +	}
> +	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;
> +}
> +
>  static int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q,
>  				    unsigned int retry)
>  {
>  	struct ap_queue_status status;
>  	int ret;
> -	int retry2 = 2;
> 
>  	if (!q)
>  		return 0;
> @@ -1629,14 +1647,8 @@ static int vfio_ap_mdev_reset_queue(struct
> vfio_ap_queue *q,
>  	}
> 
>  	/* wait for the reset to take effect */
> -	while (retry2--) {
> -		if (status.queue_empty && !status.irq_enabled)
> -			break;
> -		msleep(20);
> -		status = ap_tapq(q->apqn, NULL);
> -	}
> -	WARN_ONCE(retry2 <= 0, "unable to verify reset of queue %02x.%04x",
> -		  AP_QID_CARD(q->apqn), AP_QID_QUEUE(q->apqn));
> +	if (!status.queue_empty && status.irq_enabled)

Hm, you check for
   a) status.queue_empty and
   b) !status.irq_enabled
   which is (status.queue_empty && !status.irq_enabled)
   and now let's negate this to:
   !(status.queue_empty && !status.irq_enabled)
   with de-morgan this gives:
   (!status.queue_empty || status.irq_enabled)

> +		ret = apq_reset_check(q);
> 
>  free_resources:
>  	vfio_ap_free_aqic_resources(q);

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