linux-kernel - Re: [PATCH v6 3/7] s390: ap: setup relation betwen KVM and mediated device

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Date:   Thu, 28 Mar 2019 17:27:41 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, borntraeger@...ibm.com
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, frankja@...ux.ibm.com, pasic@...ux.ibm.com,
        david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v6 3/7] s390: ap: setup relation betwen KVM and mediated
 device

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@...ux.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.

Regards,
Pierre



-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany