Re: [PATCH v4 13/15] KVM: s390: configure the guest's AP devices

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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.


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