vfio/mtty: Enforce available_instances

The sample mtty mdev driver doesn't actually enforce the number of
device instances it claims are available.  Implement this properly.

Link: https://lore.kernel.org/r/162465624894.3338367.12935940647049917981.stgit@omen
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed by: Kirti Wankhede <kwankhede@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index ffbaf07..8b26fec 100644 (file)
--- a/samples/vfio-mdev/mtty.c
+++ b/samples/vfio-mdev/mtty.c
@@ -144,7 +144,7 @@ struct mdev_state {
        int nr_ports;
 };
 
-static atomic_t mdev_used_ports;
+static atomic_t mdev_avail_ports = ATOMIC_INIT(MAX_MTTYS);
 
 static const struct file_operations vd_fops = {
        .owner          = THIS_MODULE,
@@ -707,11 +707,20 @@ static int mtty_probe(struct mdev_device *mdev)
 {
        struct mdev_state *mdev_state;
        int nr_ports = mdev_get_type_group_id(mdev) + 1;
+       int avail_ports = atomic_read(&mdev_avail_ports);
        int ret;
 
+       do {
+               if (avail_ports < nr_ports)
+                       return -ENOSPC;
+       } while (!atomic_try_cmpxchg(&mdev_avail_ports,
+                                    &avail_ports, avail_ports - nr_ports));
+
        mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
-       if (mdev_state == NULL)
+       if (mdev_state == NULL) {
+               atomic_add(nr_ports, &mdev_avail_ports);
                return -ENOMEM;
+       }
 
        vfio_init_group_dev(&mdev_state->vdev, &mdev->dev, &mtty_dev_ops);
 
@@ -724,6 +733,7 @@ static int mtty_probe(struct mdev_device *mdev)
 
        if (mdev_state->vconfig == NULL) {
                kfree(mdev_state);
+               atomic_add(nr_ports, &mdev_avail_ports);
                return -ENOMEM;
        }
 
@@ -735,9 +745,9 @@ static int mtty_probe(struct mdev_device *mdev)
        ret = vfio_register_group_dev(&mdev_state->vdev);
        if (ret) {
                kfree(mdev_state);
+               atomic_add(nr_ports, &mdev_avail_ports);
                return ret;
        }
-       atomic_add(mdev_state->nr_ports, &mdev_used_ports);
 
        dev_set_drvdata(&mdev->dev, mdev_state);
        return 0;
@@ -746,12 +756,13 @@ static int mtty_probe(struct mdev_device *mdev)
 static void mtty_remove(struct mdev_device *mdev)
 {
        struct mdev_state *mdev_state = dev_get_drvdata(&mdev->dev);
+       int nr_ports = mdev_state->nr_ports;
 
-       atomic_sub(mdev_state->nr_ports, &mdev_used_ports);
        vfio_unregister_group_dev(&mdev_state->vdev);
 
        kfree(mdev_state->vconfig);
        kfree(mdev_state);
+       atomic_add(nr_ports, &mdev_avail_ports);
 }
 
 static int mtty_reset(struct mdev_state *mdev_state)
@@ -1271,8 +1282,7 @@ static ssize_t available_instances_show(struct mdev_type *mtype,
 {
        unsigned int ports = mtype_get_type_group_id(mtype) + 1;
 
-       return sprintf(buf, "%d\n",
-                      (MAX_MTTYS - atomic_read(&mdev_used_ports)) / ports);
+       return sprintf(buf, "%d\n", atomic_read(&mdev_avail_ports) / ports);
 }
 
 static MDEV_TYPE_ATTR_RO(available_instances);