[RESEND PATCH v8 09/11] vfio: Delete the unbound_list

Lu Baolu
2022-04-18T00:53:09Z

From: Jason Gunthorpe <jgg@nvidia.com>

commit 60720a0fc646 ("vfio: Add device tracking during unbind") added the
unbound list to plug a problem with KVM where KVM_DEV_VFIO_GROUP_DEL
relied on vfio_group_get_external_user() succeeding to return the
vfio_group from a group file descriptor. The unbound list allowed
vfio_group_get_external_user() to continue to succeed in edge cases.

However commit 5d6dee80a1e9 ("vfio: New external user group/file match")
deleted the call to vfio_group_get_external_user() during
KVM_DEV_VFIO_GROUP_DEL. Instead vfio_external_group_match_file() is used
to directly match the file descriptor to the group pointer.

This in turn avoids the call down to vfio_dev_viable() during
KVM_DEV_VFIO_GROUP_DEL and also avoids the trouble the first commit was
trying to fix.

There are no other users of vfio_dev_viable() that care about the time
after vfio_unregister_group_dev() returns, so simply delete the
unbound_list entirely.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
---
drivers/vfio/vfio.c | 74 ++-------------------------------------------
1 file changed, 2 insertions(+), 72 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 8a9347f732a5..b2f19d17d0c3 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -62,11 +62,6 @@ struct vfio_container {
bool noiommu;
};

-struct vfio_unbound_dev {
- struct device *dev;
- struct list_head unbound_next;
-};
-
struct vfio_group {
struct device dev;
struct cdev cdev;
@@ -79,8 +74,6 @@ struct vfio_group {
struct notifier_block nb;
struct list_head vfio_next;
struct list_head container_next;
- struct list_head unbound_list;
- struct mutex unbound_lock;
atomic_t opened;
wait_queue_head_t container_q;
enum vfio_group_type type;
@@ -340,16 +333,8 @@ vfio_group_get_from_iommu(struct iommu_group *iommu_group)
static void vfio_group_release(struct device *dev)
{
struct vfio_group *group = container_of(dev, struct vfio_group, dev);
- struct vfio_unbound_dev *unbound, *tmp;
-
- list_for_each_entry_safe(unbound, tmp,
- &group->unbound_list, unbound_next) {
- list_del(&unbound->unbound_next);
- kfree(unbound);
- }

mutex_destroy(&group->device_lock);
- mutex_destroy(&group->unbound_lock);
iommu_group_put(group->iommu_group);
ida_free(&vfio.group_ida, MINOR(group->dev.devt));
kfree(group);
@@ -381,8 +366,6 @@ static struct vfio_group *vfio_group_alloc(struct iommu_group *iommu_group,
refcount_set(&group->users, 1);
INIT_LIST_HEAD(&group->device_list);
mutex_init(&group->device_lock);
- INIT_LIST_HEAD(&group->unbound_list);
- mutex_init(&group->unbound_lock);
init_waitqueue_head(&group->container_q);
group->iommu_group = iommu_group;
/* put in vfio_group_release() */
@@ -571,19 +554,8 @@ static int vfio_dev_viable(struct device *dev, void *data)
struct vfio_group *group = data;
struct vfio_device *device;
struct device_driver *drv = READ_ONCE(dev->driver);
- struct vfio_unbound_dev *unbound;
- int ret = -EINVAL;

- mutex_lock(&group->unbound_lock);
- list_for_each_entry(unbound, &group->unbound_list, unbound_next) {
- if (dev == unbound->dev) {
- ret = 0;
- break;
- }
- }
- mutex_unlock(&group->unbound_lock);
-
- if (!ret || !drv || vfio_dev_driver_allowed(dev, drv))
+ if (!drv || vfio_dev_driver_allowed(dev, drv))
return 0;

device = vfio_group_get_device(group, dev);
@@ -592,7 +564,7 @@ static int vfio_dev_viable(struct device *dev, void *data)
return 0;
}

- return ret;
+ return -EINVAL;
}

/*
@@ -634,7 +606,6 @@ static int vfio_iommu_group_notifier(struct notifier_block *nb,
{
struct vfio_group *group = container_of(nb, struct vfio_group, nb);
struct device *dev = data;
- struct vfio_unbound_dev *unbound;

switch (action) {
case IOMMU_GROUP_NOTIFY_ADD_DEVICE:
@@ -663,28 +634,6 @@ static int vfio_iommu_group_notifier(struct notifier_block *nb,
__func__, iommu_group_id(group->iommu_group),
dev->driver->name);
break;
- case IOMMU_GROUP_NOTIFY_UNBOUND_DRIVER:
- dev_dbg(dev, "%s: group %d unbound from driver\n", __func__,
- iommu_group_id(group->iommu_group));
- /*
- * XXX An unbound device in a live group is ok, but we'd
- * really like to avoid the above BUG_ON by preventing other
- * drivers from binding to it. Once that occurs, we have to
- * stop the system to maintain isolation. At a minimum, we'd
- * want a toggle to disable driver auto probe for this device.
- */
-
- mutex_lock(&group->unbound_lock);
- list_for_each_entry(unbound,
- &group->unbound_list, unbound_next) {
- if (dev == unbound->dev) {
- list_del(&unbound->unbound_next);
- kfree(unbound);
- break;
- }
- }
- mutex_unlock(&group->unbound_lock);
- break;
}
return NOTIFY_OK;
}
@@ -889,29 +838,10 @@ static struct vfio_device *vfio_device_get_from_name(struct vfio_group *group,
void vfio_unregister_group_dev(struct vfio_device *device)
{
struct vfio_group *group = device->group;
- struct vfio_unbound_dev *unbound;
unsigned int i = 0;
bool interrupted = false;
long rc;

- /*
- * When the device is removed from the group, the group suddenly
- * becomes non-viable; the device has a driver (until the unbind
- * completes), but it's not present in the group. This is bad news
- * for any external users that need to re-acquire a group reference
- * in order to match and release their existing reference. To
- * solve this, we track such devices on the unbound_list to bridge
- * the gap until they're fully unbound.
- */
- unbound = kzalloc(sizeof(*unbound), GFP_KERNEL);
- if (unbound) {
- unbound->dev = device->dev;
- mutex_lock(&group->unbound_lock);
- list_add(&unbound->unbound_next, &group->unbound_list);
- mutex_unlock(&group->unbound_lock);
- }
- WARN_ON(!unbound);
-
vfio_device_put(device);
rc = try_wait_for_completion(&device->comp);
while (rc <= 0) {
--
2.25.1