linux-kernel - Re: [PATCH v8 17/22] s390: vfio-ap: zeroize the AP queues.

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Date:   Fri, 10 Aug 2018 12:49:08 +0200
From:   Pierre Morel <pmorel@...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, Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: Re: [PATCH v8 17/22] s390: vfio-ap: zeroize the AP queues.

On 10/08/2018 11:14, Cornelia Huck wrote:
> On Wed,  8 Aug 2018 10:44:27 -0400
> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
>
>> From: Tony Krowiak <akrowiak@...ux.ibm.com>
>>
>> Let's call PAPQ(ZAPQ) to zeroize a queue:
>>
>> * For each queue configured for a mediated matrix device
>>    when it is released.
>>
>> Zeroizing a queue resets the queue, clears all pending
>> messages for the queue entries and disables adapter interruptions
>> associated with the queue.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
>> Tested-by: Michael Mueller <mimu@...ux.ibm.com>
>> Tested-by: Farhan Ali <alifm@...ux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c     |   29 ++++++++++++++++++++++++++++-
>>   drivers/s390/crypto/vfio_ap_private.h |   25 +++++++++++++++++++++++++
>>   2 files changed, 53 insertions(+), 1 deletions(-)
>>
>> @@ -788,7 +812,10 @@ static void vfio_ap_mdev_release(struct mdev_device *mdev)
>>   {
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   
>> -	kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>> +	if (matrix_mdev->kvm)
>> +		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> Confused. Why is the check for matrix_mdev->kvm added here?

When using the KVM notifier we can get two notifications:
-> KVM is here / is comming
-> KVM is not here / disappearing

In the first case we initialize matrix_mdev->kvm with a pointer to KVM
In the second case we nullify the pointer.

During the open of the mediated device, the guest should have been started
or we refuse to start.

During the close of the mediated device, the guest should be there, but
we have no certitude that the guest did not disappear before the VFIO
file being closed.
Since we do not allow multiple guests using the same mediated device
this case should not happen with QEMU. But I am not sure that
a rogue user program could not stop KVM before closing the VFIO
mediated device.

Maybe Alex can confirm this point, if not we can remove the test.

Thanks

Pierre



>
>> +
>> +	vfio_ap_mdev_reset_queues(mdev, true);
>>   	vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
>>   				 &matrix_mdev->group_notifier);
>>   	matrix_mdev->kvm = NULL;


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