linux-kernel - Re: [PATCH v3 6/9] vfio: ap: register IOMMU VFIO notifier

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Date:   Tue, 19 Feb 2019 20:04:22 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     borntraeger@...ibm.com, 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, david@...hat.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, freude@...ux.ibm.com, mimu@...ux.ibm.com
Subject: Re: [PATCH v3 6/9] vfio: ap: register IOMMU VFIO notifier

On 19/02/2019 10:59, Halil Pasic wrote:
> On Fri, 15 Feb 2019 17:55:35 -0500
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
> 
>> On 2/14/19 8:51 AM, Pierre Morel wrote:
>>> To be able to use the VFIO interface to facilitate the
>>> mediated device memory pining/unpining we need to register
>>> a notifier for IOMMU.
>>>
>>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>>> ---
>>>    drivers/s390/crypto/vfio_ap_ops.c     | 64 +++++++++++++++++++++++++++++++----
>>>    drivers/s390/crypto/vfio_ap_private.h |  2 ++
>>>    2 files changed, 60 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>>> index 1851b24..6eddc2c 100644
>>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> 
> [..]
>    	struct vfio_ap_queue *q;
>>> @@ -967,12 +996,32 @@ static int vfio_ap_mdev_open(struct mdev_device *mdev)
>>>    
>>>    	ret = vfio_register_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
>>>    				     &events, &matrix_mdev->group_notifier);
>>> -	if (ret) {
>>> -		module_put(THIS_MODULE);
>>> -		return ret;
>>> -	}
>>> +	if (ret)
>>> +		goto err_group;
>>> +
>>> +	matrix_mdev->iommu_notifier.notifier_call = vfio_ap_mdev_iommu_notifier;
>>> +	events = VFIO_IOMMU_NOTIFY_DMA_UNMAP;
>>> +
>>> +	ret = vfio_register_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
>>> +				     &events, &matrix_mdev->iommu_notifier);
>>> +	if (ret)
>>> +		goto err_iommu;
>>> +
>>> +	ret = vfio_ap_associate_queues(matrix_mdev);
>>> +	if (ret)
>>> +		goto err_associate;
>>
>> I think the matrix_mdev should be associated with queues when an
>> assignment of an adapter or domain is made to the mdev device via its
>> sysfs interfaces. I say this because assigning an adapter or domain to
>> an mdev device effectively grants ownership of any additional AP queues
>> added to the mdev device's AP matrix as a result of the assignment. It
>> only makes sense to assign ownership to the vfio_ap_queue objects
>> representing the queues at that time. If an adapter or domain is
>> dynamically assigned while a guest is using the affected queues, then
>> the associations will have to be made at that time and this code will
>> likely go bye bye.
>>
> 
> 
> Actually, we need the stuff in vfio_ap_queues only if the guest is
> offered to  decides to use AP adaper interrupts. I would prefer to have
> it around only when needed: as long as we have the nib pinned for any
> given queue. Is there a reason why not to do so?
> 
> Regards,
> Halil
>   
> [..]
> 

Since I will rework the vfio_ap_queue life cycle, I will study this.
But I find the creation / deletion in probe/remove and the link/unlimk 
to the matrix device in assign/un_assign as suggested by Tony more logical.

Regards,
Pierre

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