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Subject[PATCH] vfio/mtty: Enforce available_instances
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Date
The sample mtty mdev driver doesn't actually enforce the number of
device instances it claims are available. Implement this properly.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

Applies to vfio next branch + Jason's atomic conversion

samples/vfio-mdev/mtty.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
index ffbaf07a17ea..8b26fecc4afe 100644
--- 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);

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