Re: [PATCH 9/9] vfio: Remove calls to vfio_group_add_container_user()

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Apr 13, 2022 at 08:11:05AM +0200, Christoph Hellwig wrote:
> On Tue, Apr 12, 2022 at 12:53:36PM -0300, Jason Gunthorpe wrote:
> > +	if (WARN_ON(!READ_ONCE(vdev->open_count)))
> > +		return -EINVAL;
> 
> I think all the WARN_ON()s in this patch need to be WARN_ON_ONCE,
> otherwise there will be too many backtraces to be useful if a driver
> ever gets the API wrong.

Sure, I added a wrapper to make that have less overhead and merged it
with the other 'driver is calling this correctly' checks:

@@ -1330,6 +1330,12 @@ static int vfio_group_add_container_user(struct vfio_group *group)
 
 static const struct file_operations vfio_device_fops;
 
+/* true if the vfio_device has open_device() called but not close_device() */
+static bool vfio_assert_device_open(struct vfio_device *device)
+{
+	return !WARN_ON_ONCE(!READ_ONCE(device->open_count));
+}
+
 static int vfio_group_get_device_fd(struct vfio_group *group, char *buf)
 {
 	struct vfio_device *device;
@@ -1544,6 +1550,7 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
 	struct vfio_device *device = filep->private_data;
 
 	mutex_lock(&device->dev_set->lock);
+	vfio_assert_device_open(device);
 	if (!--device->open_count && device->ops->close_device)
 		device->ops->close_device(device);
 	mutex_unlock(&device->dev_set->lock);
@@ -2112,7 +2119,7 @@ int vfio_pin_pages(struct vfio_device *vdev, unsigned long *user_pfn, int npage,
 	struct vfio_iommu_driver *driver;
 	int ret;
 
-	if (!user_pfn || !phys_pfn || !npage)
+	if (!user_pfn || !phys_pfn || !npage || !vfio_assert_device_open(vdev))
 		return -EINVAL;
 
 	if (npage > VFIO_PIN_PAGES_MAX_ENTRIES)
@@ -2121,9 +2128,6 @@ int vfio_pin_pages(struct vfio_device *vdev, unsigned long *user_pfn, int npage,
 	if (group->dev_counter > 1)
 		return -EINVAL;
 
-	if (WARN_ON(!READ_ONCE(vdev->open_count)))
-		return -EINVAL;
-
 	container = group->container;
 	driver = container->iommu_driver;
 	if (likely(driver && driver->ops->pin_pages))
@@ -2153,15 +2157,12 @@ int vfio_unpin_pages(struct vfio_device *vdev, unsigned long *user_pfn,
 	struct vfio_iommu_driver *driver;
 	int ret;
 
-	if (!user_pfn || !npage)
+	if (!user_pfn || !npage || !vfio_assert_device_open(vdev))
 		return -EINVAL;
 
 	if (npage > VFIO_PIN_PAGES_MAX_ENTRIES)
 		return -E2BIG;
 
-	if (WARN_ON(!READ_ONCE(vdev->open_count)))
-		return -EINVAL;
-
 	container = vdev->group->container;
 	driver = container->iommu_driver;
 	if (likely(driver && driver->ops->unpin_pages))
@@ -2198,10 +2199,7 @@ int vfio_dma_rw(struct vfio_device *vdev, dma_addr_t user_iova,
 	struct vfio_iommu_driver *driver;
 	int ret = 0;
 
-	if (!data || len <= 0)
-		return -EINVAL;
-
-	if (WARN_ON(!READ_ONCE(vdev->open_count)))
+	if (!data || len <= 0 || !vfio_assert_device_open(vdev))
 		return -EINVAL;
 
 	container = vdev->group->container;
@@ -2294,10 +2292,7 @@ int vfio_register_notifier(struct vfio_device *dev, enum vfio_notify_type type,
 	struct vfio_group *group = dev->group;
 	int ret;
 
-	if (!nb || !events || (*events == 0))
-		return -EINVAL;
-
-	if (WARN_ON(!READ_ONCE(dev->open_count)))
+	if (!nb || !events || (*events == 0) || !vfio_assert_device_open(dev))
 		return -EINVAL;
 
 	switch (type) {
@@ -2321,10 +2316,7 @@ int vfio_unregister_notifier(struct vfio_device *dev,
 	struct vfio_group *group = dev->group;
 	int ret;
 
-	if (!nb)
-		return -EINVAL;
-
-	if (WARN_ON(!READ_ONCE(dev->open_count)))
+	if (!nb || !vfio_assert_device_open(dev))
 		return -EINVAL;
 
 	switch (type) {

Thanks,
Jason