linux-kernel - [PATCH] s390/vfio-ap: fix unregister GISC when KVM is already gone results in OOPS

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Message-Id: <20200918170234.5807-1-akrowiak@linux.ibm.com>
Date:   Fri, 18 Sep 2020 13:02:34 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     pmorel@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, cohuck@...hat.com,
        kwankhede@...dia.com, borntraeger@...ibm.com,
        Tony Krowiak <akrowiak@...ux.ibm.com>
Subject: [PATCH] s390/vfio-ap: fix unregister GISC when KVM is already gone results in OOPS

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 <akrowiak@...ux.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;
 }
-- 
2.21.1