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Subject: Re: [PATCH v6 3/7] s390: ap: setup relation betwen KVM and mediated
 device
To:     pmorel@linux.ibm.com, borntraeger@de.ibm.com
Cc:     alex.williamson@redhat.com, cohuck@redhat.com,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        kvm@vger.kernel.org, frankja@linux.ibm.com, pasic@linux.ibm.com,
        david@redhat.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, freude@linux.ibm.com, mimu@linux.ibm.com
References: <1553265828-27823-1-git-send-email-pmorel@linux.ibm.com>
 <1553265828-27823-4-git-send-email-pmorel@linux.ibm.com>
 <1ea236d1-ca0b-03c0-3699-0c0deb435785@linux.ibm.com>
 <3cd496d0-3eec-78e8-9ea5-4d62fe0cff1c@linux.ibm.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Date:   Thu, 28 Mar 2019 13:25:35 -0400
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On 3/28/19 12:27 PM, Pierre Morel wrote:
> On 28/03/2019 17:12, Tony Krowiak wrote:
>> On 3/22/19 10:43 AM, Pierre Morel wrote:
>>> When the mediated device is open we setup the relation with KVM unset it
>>> when the mediated device is released.
>>
>> s/open we setup/open, we set up/
>> s/with KVM unset/with KVM and unset/
>>
>>>
>>> We lock the matrix mediated device to avoid any change until the
>>> open is done.
>>> We make sure that KVM is present when opening the mediated device
>>> otherwise we return an error.
>>
>> s/mediated device/mediated device,/
>>
>>>
>>> Increase kvm's refcount to ensure the KVM structures are still available
>>> during the use of the mediated device by the guest.
>>>
>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>> ---
>>>   drivers/s390/crypto/vfio_ap_ops.c | 143 
>>> +++++++++++++++++++++-----------------
>>>   1 file changed, 79 insertions(+), 64 deletions(-)
>>>
>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
>>> b/drivers/s390/crypto/vfio_ap_ops.c
>>> index 77f7bac..bdb36e0 100644
>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>>> @@ -787,74 +787,24 @@ static const struct attribute_group 
>>> *vfio_ap_mdev_attr_groups[] = {
>>>       NULL
>>>   };
>>> -/**
>>> - * vfio_ap_mdev_set_kvm
>>> - *
>>> - * @matrix_mdev: a mediated matrix device
>>> - * @kvm: reference to KVM instance
>>> - *
>>> - * Verifies no other mediated matrix device has @kvm and sets a 
>>> reference to
>>> - * it in @matrix_mdev->kvm.
>>> - *
>>> - * Return 0 if no other mediated matrix device has a reference to @kvm;
>>> - * otherwise, returns an -EPERM.
>>> - */
>>> -static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>> -                struct kvm *kvm)
>>> -{
>>> -    struct ap_matrix_mdev *m;
>>> -
>>> -    mutex_lock(&matrix_dev->lock);
>>> -
>>> -    list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>>> -        if ((m != matrix_mdev) && (m->kvm == kvm)) {
>>> -            mutex_unlock(&matrix_dev->lock);
>>> -            return -EPERM;
>>> -        }
>>> -    }
>>> -
>>> -    matrix_mdev->kvm = kvm;
>>> -    mutex_unlock(&matrix_dev->lock);
>>> -
>>> -    return 0;
>>> -}
>>> -
>>>   static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>>>                          unsigned long action, void *data)
>>>   {
>>> -    int ret;
>>>       struct ap_matrix_mdev *matrix_mdev;
>>>       if (action != VFIO_GROUP_NOTIFY_SET_KVM)
>>>           return NOTIFY_OK;
>>>       matrix_mdev = container_of(nb, struct ap_matrix_mdev, 
>>> group_notifier);
>>> -
>>> -    if (!data) {
>>> -        matrix_mdev->kvm = NULL;
>>> -        return NOTIFY_OK;
>>> -    }
>>> -
>>> -    ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
>>> -    if (ret)
>>> -        return NOTIFY_DONE;
>>> -
>>> -    /* If there is no CRYCB pointer, then we can't copy the masks */
>>> -    if (!matrix_mdev->kvm->arch.crypto.crycbd)
>>> -        return NOTIFY_DONE;
>>> -
>>> -    kvm_arch_crypto_set_masks(matrix_mdev->kvm, 
>>> matrix_mdev->matrix.apm,
>>> -                  matrix_mdev->matrix.aqm,
>>> -                  matrix_mdev->matrix.adm);
>>> +    matrix_mdev->kvm = data;
>>>       return NOTIFY_OK;
>>>   }
>>> -static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev)
>>> +static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev 
>>> *matrix_mdev)
>>>   {
>>>       int ret;
>>>       int rc = 0;
>>> -    struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>>       struct vfio_ap_queue *q;
>>>       list_for_each_entry(q, &matrix_mdev->qlist, list) {
>>> @@ -871,41 +821,106 @@ static int vfio_ap_mdev_reset_queues(struct 
>>> mdev_device *mdev)
>>>       return rc;
>>>   }
>>> +/**
>>> + * vfio_ap_mdev_set_kvm
>>> + *
>>> + * @matrix_mdev: a mediated matrix device
>>> + *
>>> + * - Verifies that the hook is free and install the PQAP hook
>>> + * - Copy the matrix masks inside the CRYCB
>>> + * - Increment the KVM rerference count
>>> + *
>>> + * Return 0 if no other mediated matrix device has a reference to @kvm;
>>> + * otherwise, returns an -EPERM.
>>> + */
>>> +static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev)
>>> +{
>>> +    if (matrix_mdev->kvm->arch.crypto.pqap_hook)
>>> +        return -EPERM;
>>
>> How would this happen; in other words, why are we checking this?
> 
> I check this to verify that no other AP mediated device is already in 
> use by this VM.

Maybe you should insert a comment to that effect.

> 
> Regards,
> Pierre
> 
> 
>