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Subject: Re: [PATCH] s390/vfio-ap: do not use open locks during
 VFIO_GROUP_NOTIFY_SET_KVM notification
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        borntraeger@de.ibm.com, cohuck@redhat.com,
        pasic@linux.vnet.ibm.com, jjherne@linux.ibm.com,
        alex.williamson@redhat.com, kwankhede@nvidia.com,
        frankja@linux.ibm.com, david@redhat.com, imbrenda@linux.ibm.com,
        hca@linux.ibm.com
References: <20210625220758.80365-1-akrowiak@linux.ibm.com>
 <20210628173448.GG4459@nvidia.com>
 <cc14f238-ba11-e388-06ec-027912fc313c@linux.ibm.com>
 <20210628182248.GH4459@nvidia.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Message-ID: <f098fc11-d328-8130-bab9-bf38e18a7400@linux.ibm.com>
Date:   Mon, 28 Jun 2021 14:27:26 -0400
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On 6/28/21 2:22 PM, Jason Gunthorpe wrote:
> On Mon, Jun 28, 2021 at 02:20:55PM -0400, Tony Krowiak wrote:
>>
>> On 6/28/21 1:34 PM, Jason Gunthorpe wrote:
>>> On Fri, Jun 25, 2021 at 06:07:58PM -0400, Tony Krowiak wrote:
>>>>    static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>>>>    {
>>>> +	mutex_lock(&matrix_dev->lock);
>>>> +	if ((matrix_mdev->kvm) && (matrix_mdev->kvm->arch.crypto.crycbd)) {
>>>>    		mutex_unlock(&matrix_dev->lock);
>>>> +		down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>>>> +		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>>> +		up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>>>> +		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>>>>    		mutex_lock(&matrix_dev->lock);
>>>>    		vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
>>>>    		kvm_put_kvm(matrix_mdev->kvm);
>>>>    		matrix_mdev->kvm = NULL;
>>>> +		mutex_unlock(&matrix_dev->lock);
>>>>    	}
>>> Doesn't a flow exit the function with matrix_dev->lock held he

Yes, you are correct. Stupid mistake.

>> How can that happen? What flow?
> When the if isn't taken
>
>>> Write it with 'success oriented flow'
>> I'm not sure what you mean, can you clarify this statement?
> Basically, don't write the bulk of the function under an if statement
>
> mutex_lock(&matrix_dev->lock);
> if (!matrix_mdev->kvm || !matrix_mdev->kvm->arch.crypto.crycbd) {
>      mutex_unlock(&matrix_dev->lock);
>      return;
> }

Sure.

>
> Jason
>