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

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Date:   Fri, 10 Aug 2018 13:16:48 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     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, Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: Re: [PATCH v8 17/22] s390: vfio-ap: zeroize the AP queues.

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 :)

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