linux-kernel - Re: [PATCH v9 15/22] s390: vfio-ap: implement mediated device open callback

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Date:   Wed, 15 Aug 2018 14:21:27 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v9 15/22] s390: vfio-ap: implement mediated device open
 callback

On 08/15/2018 12:08 PM, Cornelia Huck wrote:
> On Mon, 13 Aug 2018 17:48:12 -0400
> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
>
>> From: Tony Krowiak <akrowiak@...ux.ibm.com>
>>
>> Implements the open callback on the mediated matrix device.
>> The function registers a group notifier to receive notification
>> of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
>> the vfio_ap device driver will get access to the guest's
>> kvm structure. The open callback must ensure that only one
>> mediated device shall be opened per guest.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> Acked-by: Halil Pasic <pasic@...ux.ibm.com>
>> Tested-by: Michael Mueller <mimu@...ux.ibm.com>
>> Tested-by: Farhan Ali <alifm@...ux.ibm.com>
>> Tested-by: Pierre Morel <pmorel@...ux.ibm.com>
>> Acked-by: Pierre Morel <pmorel@...ux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c     |  174 ++++++++++++++++++++++++++++++++-
>>   drivers/s390/crypto/vfio_ap_private.h |    2 +
>>   2 files changed, 175 insertions(+), 1 deletions(-)
>> @@ -602,7 +633,6 @@ static ssize_t matrix_show(struct device *dev, struct device_attribute *attr,
>>   }
>>   DEVICE_ATTR_RO(matrix);
>>   
>> -
> Nit: whitespace change

A nit, but somebody else will point it out too, so I will fix it.

>
>>   static struct attribute *vfio_ap_mdev_attrs[] = {
>>   	&dev_attr_assign_adapter.attr,
>>   	&dev_attr_unassign_adapter.attr,
> (...)
>
>> +/**
>> + * vfio_ap_mdev_open_once
>> + *
>> + * @matrix_mdev: a mediated matrix device
>> + *
>> + * Return 0 if no other mediated matrix device has been opened for the
>> + * KVM guest assigned to @matrix_mdev; otherwise, returns an error.
>> + */
>> +static int vfio_ap_mdev_open_once(struct ap_matrix_mdev *matrix_mdev,
>> +				  struct kvm *kvm)
> You're passing kvm in here, but do not use it.

I'll fix it.

>
>> +{
>> +	struct ap_matrix_mdev *m;
>> +
>> +	mutex_lock(&matrix_dev.lock);
>> +
>> +	list_for_each_entry(m, &matrix_dev.mdev_list, list) {
>> +		if ((m != matrix_mdev) && (m->kvm == matrix_mdev->kvm)) {
> If you used it here instead of matrix_mdev->kvm...

I believe that was the case in a previous patch, but for some reason the 
code
was changed. I'll rework this so it uses the kvm param instead.

>
>> +			mutex_unlock(&matrix_dev.lock);
>> +			return -EPERM;
>> +		}
>> +	}
>> +
>> +	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);
>> +
>> +	matrix_mdev->kvm = data;
>> +	if (data == NULL)
>> +		return NOTIFY_OK;
>> +
>> +	ret = vfio_ap_mdev_open_once(matrix_mdev, data);
> ...you could move this up to before overwriting matrix_mdev->kvm and
> bailing out when the check failed, which makes more sense to me.

That makes more sense to me too. Don't set matrix_mdev->kvm until we
know it is okay to do so.

>
>> +	if (ret)
>> +		return ret;
>> +
>> +	ret = kvm_ap_validate_crypto_setup(matrix_mdev->kvm);
>> +	if (ret)
>> +		return ret;
> It probably makes more sense to return NOTIFY_DONE in the error case
> (NOTIFY_BAD does not sound like a good idea as it would stop processing
> the notifier chain).

Will do.

>
>> +
>> +	vfio_ap_mdev_copy_masks(matrix_mdev);
>> +
>> +	return NOTIFY_OK;
>> +}
> Otherwise, looks sane.

Good!!!

>