From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tony Krowiak <akrowiak@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 13/15] KVM: s390: configure the guest's AP devices
Date: Tue, 17 Apr 2018 12:12:35 -0400
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To: Halil Pasic <pasic@linux.vnet.ibm.com>, Pierre Morel <pmorel@linux.vnet.ibm.com>, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org
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On 04/16/2018 10:51 AM, Halil Pasic wrote:
>
> On 04/16/2018 03:05 PM, Pierre Morel wrote:
>>> +static void vfio_ap_mdev_release(struct mdev_device *mdev)
>>> +{
>>> +    struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>> +
>>> +    kvm_ap_deconfigure_matrix(matrix_mdev->kvm);
>>> +    kvm_ap_interpret_instructions(matrix_mdev->kvm, false);
>> This call clears the apie in KVM.
>> This is only OK if we have a single device present until the end of the VM,
>> otherwise AP instructions in the guest will fail after the release until the end of the VM
>> or until a new device is plugged.
> I agree, this seems wrong.

As I think about this more, you may be correct. I believe that one can 
remove a VFIO mediated
device via a sysfs file descriptor. I suppose that could happen while 
the guest is still running,
which would mean AP instructions executed on the guest would meet with 
an operation exception.
I will have to explore this some more.