In trying to recreate this problem in order to get a stack trace, I discovered that it only occurs within a local repository that has several new patches applied, so the problem is not part of the base code and will be fixed via this new set
of patches forthcoming.

On 9/18/20 1:02 PM, Tony Krowiak wrote:
Attempting to unregister Guest Interruption Subclass (GISC) when the
link between the matrix mdev and KVM has been removed results in the
following:

    "Kernel panic -not syncing: Fatal exception: panic_on_oops"

This patch fixes this bug by verifying the matrix mdev and KVM are still
linked prior to unregistering the GISC.

Signed-off-by: Tony Krowiak <akrow...@linux.ibm.com>
---
  drivers/s390/crypto/vfio_ap_ops.c | 14 +++++++++-----
  1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c 
b/drivers/s390/crypto/vfio_ap_ops.c
index e0bde8518745..847a88642644 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -119,11 +119,15 @@ static void vfio_ap_wait_for_irqclear(int apqn)
   */
  static void vfio_ap_free_aqic_resources(struct vfio_ap_queue *q)
  {
-       if (q->saved_isc != VFIO_AP_ISC_INVALID && q->matrix_mdev)
-               kvm_s390_gisc_unregister(q->matrix_mdev->kvm, q->saved_isc);
-       if (q->saved_pfn && q->matrix_mdev)
-               vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev),
-                                &q->saved_pfn, 1);
+       if (q->matrix_mdev) {
+               if (q->saved_isc != VFIO_AP_ISC_INVALID && q->matrix_mdev->kvm)
+                       kvm_s390_gisc_unregister(q->matrix_mdev->kvm,
+                                                q->saved_isc);
+               if (q->saved_pfn)
+                       vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev),
+                                        &q->saved_pfn, 1);
+       }
+
        q->saved_pfn = 0;
        q->saved_isc = VFIO_AP_ISC_INVALID;
  }

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