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From:   Tony Krowiak <akrowiak@linux.ibm.com>
To:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     jjherne@linux.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com,
        mjrosato@linux.ibm.com, pasic@linux.ibm.com,
        alex.williamson@redhat.com, kwankhede@nvidia.com,
        fiuczy@linux.ibm.com
Subject: [PATCH 1/2] s390/vfio-ap: fix hang during removal of mdev after duplicate assignment
Date:   Wed, 17 Aug 2022 18:52:41 -0400
Message-Id: <20220817225242.188805-2-akrowiak@linux.ibm.com>
In-Reply-To: <20220817225242.188805-1-akrowiak@linux.ibm.com>
References: <20220817225242.188805-1-akrowiak@linux.ibm.com>
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When the same adapter or domain is assigned more than one time prior to
removing the matrix mdev to which it is assigned, the remove operation
will hang. The reason is because the same vfio_ap_queue objects with an
APQN containing the APID of the adapter or APQI of the domain being
assigned will get added to the hashtable that holds them multiple times.
This results in the pprev and next pointers of the hlist_node (mdev_qnode
field in the vfio_ap_queue object) pointing to the queue object itself.
This causes an interminable loop when the mdev is removed and the queue
table is iterated to reset the queues.

To fix this problem, the assignment operation is bypassed when assigning
an adapter or domain if it is already assigned to the matrix mdev.

Since it is not necessary to assign a resource already assigned or to
unassign a resource that has not been assigned, this patch will bypass
all assignment/unassignment operations for an adapter, domain or
control domain under these circumstances.

Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 6c8c41fac4e1..ee82207b4e60 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -984,6 +984,11 @@ static ssize_t assign_adapter_store(struct device *dev,
 		goto done;
 	}
 
+	if (test_bit_inv(apid, matrix_mdev->matrix.apm)) {
+		ret = count;
+		goto done;
+	}
+
 	set_bit_inv(apid, matrix_mdev->matrix.apm);
 
 	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
@@ -1109,6 +1114,11 @@ static ssize_t unassign_adapter_store(struct device *dev,
 		goto done;
 	}
 
+	if (!test_bit_inv(apid, matrix_mdev->matrix.apm)) {
+		ret = count;
+		goto done;
+	}
+
 	clear_bit_inv((unsigned long)apid, matrix_mdev->matrix.apm);
 	vfio_ap_mdev_hot_unplug_adapter(matrix_mdev, apid);
 	ret = count;
@@ -1183,6 +1193,11 @@ static ssize_t assign_domain_store(struct device *dev,
 		goto done;
 	}
 
+	if (test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
+		ret = count;
+		goto done;
+	}
+
 	set_bit_inv(apqi, matrix_mdev->matrix.aqm);
 
 	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
@@ -1286,6 +1301,11 @@ static ssize_t unassign_domain_store(struct device *dev,
 		goto done;
 	}
 
+	if (!test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
+		ret = count;
+		goto done;
+	}
+
 	clear_bit_inv((unsigned long)apqi, matrix_mdev->matrix.aqm);
 	vfio_ap_mdev_hot_unplug_domain(matrix_mdev, apqi);
 	ret = count;
@@ -1329,6 +1349,11 @@ static ssize_t assign_control_domain_store(struct device *dev,
 		goto done;
 	}
 
+	if (test_bit_inv(id, matrix_mdev->matrix.adm)) {
+		ret = count;
+		goto done;
+	}
+
 	/* Set the bit in the ADM (bitmask) corresponding to the AP control
 	 * domain number (id). The bits in the mask, from most significant to
 	 * least significant, correspond to IDs 0 up to the one less than the
@@ -1378,6 +1403,11 @@ static ssize_t unassign_control_domain_store(struct device *dev,
 		goto done;
 	}
 
+	if (!test_bit_inv(domid, matrix_mdev->matrix.adm)) {
+		ret = count;
+		goto done;
+	}
+
 	clear_bit_inv(domid, matrix_mdev->matrix.adm);
 
 	if (test_bit_inv(domid, matrix_mdev->shadow_apcb.adm)) {
-- 
2.31.1