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

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Date:   Fri, 10 Aug 2018 12:24:47 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        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 v8 17/22] s390: vfio-ap: zeroize the AP queues.

On 08/10/2018 07:16 AM, Cornelia Huck wrote:
> On Fri, 10 Aug 2018 12:49:08 +0200
> Pierre Morel <pmorel@...ux.ibm.com> wrote:
>
>> 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.
> I'm not sure why the check is introduced in this patch, though. But
> maybe I just need weekend :)

Good catch, it belongs in patch 15 where the function is introduced.
Is that the only reason for your objection?

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