linux-kernel - Re: [PATCH v4 1/1] s390/vfio-ap: fix circular lockdep when setting/clearing crypto masks

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Date:   Thu, 18 Mar 2021 14:38:53 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, stable@...r.kernel.org,
        borntraeger@...ibm.com, cohuck@...hat.com, kwankhede@...dia.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pasic@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 1/1] s390/vfio-ap: fix circular lockdep when
 setting/clearing crypto masks



On 3/17/21 7:17 PM, Halil Pasic wrote:
> On Wed, 10 Mar 2021 10:05:59 -0500
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>
>> -		ret = vfio_ap_mdev_reset_queues(mdev);
>> +		matrix_mdev = mdev_get_drvdata(mdev);
> Is it guaranteed that matrix_mdev can't be NULL here? If yes, please
> remind me of the mechanism that ensures this.
>
>> +
>> +		/*
>> +		 * If the KVM pointer is in the process of being set, wait until
>> +		 * the process has completed.
>> +		 */
>> +		wait_event_cmd(matrix_mdev->wait_for_kvm,
>> +			       matrix_mdev->kvm_busy == false,
>> +			       mutex_unlock(&matrix_dev->lock),
>> +			       mutex_lock(&matrix_dev->lock));
>> +
>> +		if (matrix_mdev->kvm)
>> +			ret = vfio_ap_mdev_reset_queues(mdev);
>> +		else
>> +			ret = -ENODEV;
> Didn't we agree to make the call to vfio_ap_mdev_reset_queues()
> unconditional again (for reference please take look at
> Message-ID: <64afa72c-2d6a-2ca1-e576-34e15fa579ed@...ux.ibm.com>)?

How about this:

static ssize_t vfio_ap_mdev_ioctl(struct mdev_device *mdev,
                     unsigned int cmd, unsigned long arg)
{
     int ret = 0;
     struct ap_matrix_mdev *matrix_mdev;

     ...
     case VFIO_DEVICE_RESET:
         matrix_mdev = mdev_get_drvdata(mdev);
         WARN(!matrix_mdev, "Driver data missing from mdev!!");

         if (matrix_mdev) {
             /*
              * If the KVM pointer is in the process of being set, wait 
until
              * the process has completed.
              */
             wait_event_cmd(matrix_mdev->wait_for_kvm,
                        matrix_mdev->kvm_busy == false,
mutex_unlock(&matrix_dev->lock),
mutex_lock(&matrix_dev->lock));

             ret = vfio_ap_mdev_reset_queues(mdev);
         }
         break;
     ...

     return ret;
}

>
> Regards,
> Halil