vfio/mdev: add mdev available instance checking to the core

Many of the mdev drivers use a simple counter for keeping track of the
available instances. Move this code to the core code and store the counter
in the mdev_parent. Implement it using correct locking, fixing mdpy.

Drivers just provide the value in the mdev_driver at registration time
and the core code takes care of maintaining it and exposing the value in
sysfs.

[hch: count instances per-parent instead of per-type, use an atomic_t
 to avoid taking mdev_list_lock in the show method]

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Link: https://lore.kernel.org/r/20220923092652.100656-15-hch@lst.de
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

5 files changed, 2 insertions, 31 deletions

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index e5f21c725326..7f5402fe857a 100644
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -141,7 +141,6 @@ static struct vfio_ccw_private *vfio_ccw_alloc_private(struct subchannel *sch)
 	INIT_LIST_HEAD(&private->crw);
 	INIT_WORK(&private->io_work, vfio_ccw_sch_io_todo);
 	INIT_WORK(&private->crw_work, vfio_ccw_crw_todo);
-	atomic_set(&private->avail, 1);
 
 	private->cp.guest_cp = kcalloc(CCWCHAIN_LEN_MAX, sizeof(struct ccw1),
 				       GFP_KERNEL);
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index 559ca1805592..6ae4d012d800 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -44,13 +44,6 @@ static void vfio_ccw_dma_unmap(struct vfio_device *vdev, u64 iova, u64 length)
 	vfio_ccw_mdev_reset(private);
 }
 
-static unsigned int vfio_ccw_get_available(struct mdev_type *mtype)
-{
-	struct vfio_ccw_private *private = dev_get_drvdata(mtype->parent->dev);
-
-	return atomic_read(&private->avail);
-}
-
 static int vfio_ccw_mdev_init_dev(struct vfio_device *vdev)
 {
 	struct vfio_ccw_private *private =
@@ -68,9 +61,6 @@ static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
 	if (private->state == VFIO_CCW_STATE_NOT_OPER)
 		return -ENODEV;
 
-	if (atomic_dec_if_positive(&private->avail) < 0)
-		return -EPERM;
-
 	ret = vfio_init_device(&private->vdev, &mdev->dev, &vfio_ccw_dev_ops);
 	if (ret)
 		return ret;
@@ -88,7 +78,6 @@ static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
 
 err_put_vdev:
 	vfio_put_device(&private->vdev);
-	atomic_inc(&private->avail);
 	return ret;
 }
 
@@ -130,8 +119,6 @@ static void vfio_ccw_mdev_remove(struct mdev_device *mdev)
 	 * cycle.
 	 */
 	wait_for_completion(&private->release_comp);
-
-	atomic_inc(&private->avail);
 }
 
 static int vfio_ccw_mdev_open_device(struct vfio_device *vdev)
@@ -605,6 +592,7 @@ static const struct vfio_device_ops vfio_ccw_dev_ops = {
 
 struct mdev_driver vfio_ccw_mdev_driver = {
 	.device_api = VFIO_DEVICE_API_CCW_STRING,
+	.max_instances = 1,
 	.driver = {
 		.name = "vfio_ccw_mdev",
 		.owner = THIS_MODULE,
@@ -612,5 +600,4 @@ struct mdev_driver vfio_ccw_mdev_driver = {
 	},
 	.probe = vfio_ccw_mdev_probe,
 	.remove = vfio_ccw_mdev_remove,
-	.get_available = vfio_ccw_get_available,
 };
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index 52caa721ec06..bd5fb81456af 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -73,7 +73,6 @@ struct vfio_ccw_crw {
  * @sch: pointer to the subchannel
  * @state: internal state of the device
  * @completion: synchronization helper of the I/O completion
- * @avail: available for creating a mediated device
  * @io_region: MMIO region to input/output I/O arguments/results
  * @io_mutex: protect against concurrent update of I/O regions
  * @region: additional regions for other subchannel operations
@@ -97,7 +96,6 @@ struct vfio_ccw_private {
 	struct subchannel	*sch;
 	int			state;
 	struct completion	*completion;
-	atomic_t		avail;
 	struct ccw_io_region	*io_region;
 	struct mutex		io_mutex;
 	struct vfio_ccw_region *region;
diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 8606f5d75188..2884189f3877 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -689,9 +689,6 @@ static int vfio_ap_mdev_init_dev(struct vfio_device *vdev)
 	struct ap_matrix_mdev *matrix_mdev =
 		container_of(vdev, struct ap_matrix_mdev, vdev);
 
-	if ((atomic_dec_if_positive(&matrix_dev->available_instances) < 0))
-		return -EPERM;
-
 	matrix_mdev->mdev = to_mdev_device(vdev->dev);
 	vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
 	matrix_mdev->pqap_hook = handle_pqap;
@@ -770,7 +767,6 @@ static void vfio_ap_mdev_unlink_fr_queues(struct ap_matrix_mdev *matrix_mdev)
 
 static void vfio_ap_mdev_release_dev(struct vfio_device *vdev)
 {
-	atomic_inc(&matrix_dev->available_instances);
 	vfio_free_device(vdev);
 }
 
@@ -790,11 +786,6 @@ static void vfio_ap_mdev_remove(struct mdev_device *mdev)
 	vfio_put_device(&matrix_mdev->vdev);
 }
 
-static unsigned int vfio_ap_mdev_get_available(struct mdev_type *mtype)
-{
-	return atomic_read(&matrix_dev->available_instances);
-}
-
 #define MDEV_SHARING_ERR "Userspace may not re-assign queue %02lx.%04lx " \
 			 "already assigned to %s"
 
@@ -1772,6 +1763,7 @@ static const struct vfio_device_ops vfio_ap_matrix_dev_ops = {
 
 static struct mdev_driver vfio_ap_matrix_driver = {
 	.device_api = VFIO_DEVICE_API_AP_STRING,
+	.max_instances = MAX_ZDEV_ENTRIES_EXT,
 	.driver = {
 		.name = "vfio_ap_mdev",
 		.owner = THIS_MODULE,
@@ -1780,15 +1772,12 @@ static struct mdev_driver vfio_ap_matrix_driver = {
 	},
 	.probe = vfio_ap_mdev_probe,
 	.remove = vfio_ap_mdev_remove,
-	.get_available = vfio_ap_mdev_get_available,
 };
 
 int vfio_ap_mdev_register(void)
 {
 	int ret;
 
-	atomic_set(&matrix_dev->available_instances, MAX_ZDEV_ENTRIES_EXT);
-
 	ret = mdev_register_driver(&vfio_ap_matrix_driver);
 	if (ret)
 		return ret;
diff --git a/drivers/s390/crypto/vfio_ap_private.h b/drivers/s390/crypto/vfio_ap_private.h
index 441dc8dda380..2eddd5f34ed3 100644
--- a/drivers/s390/crypto/vfio_ap_private.h
+++ b/drivers/s390/crypto/vfio_ap_private.h
@@ -29,7 +29,6 @@
  * struct ap_matrix_dev - Contains the data for the matrix device.
  *
  * @device:	generic device structure associated with the AP matrix device
- * @available_instances: number of mediated matrix devices that can be created
  * @info:	the struct containing the output from the PQAP(QCI) instruction
  * @mdev_list:	the list of mediated matrix devices created
  * @mdevs_lock: mutex for locking the AP matrix device. This lock will be
@@ -46,7 +45,6 @@
  */
 struct ap_matrix_dev {
 	struct device device;
-	atomic_t available_instances;
 	struct ap_config_info info;
 	struct list_head mdev_list;
 	struct mutex mdevs_lock; /* serializes access to each ap_matrix_mdev */