[PATCH v2] vfio: Remove vfio_group dev_counter

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This counts the number of devices attached to a vfio_group, ie the number
of items in the group->device_list.

It is only read in vfio_pin_pages(), as some kind of protection against
limitations in type1.

However, with all the code cleanups in this area, now that
vfio_pin_pages() accepts a vfio_device directly it is redundant.  All
drivers are already calling vfio_register_emulated_iommu_dev() which
directly creates a group specifically for the device and thus it is
guaranteed that there is a singleton group.

Leave a note in the comment about this requirement and remove the logic.

Reviewed-by: Yi Liu <yi.l.liu@xxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 drivers/vfio/vfio_main.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

v2:
 - Reword commit message
 - Add a note in the comment that vfio_register_emulated_iommu_dev() must
    be used
v1: https://lore.kernel.org/r/0-v1-efa4029ed93d+22-vfio_dev_counter_jgg@xxxxxxxxxx

diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 7cb56c382c97a2..94a76cb86a0388 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -74,7 +74,6 @@ struct vfio_group {
 	struct list_head		vfio_next;
 	struct list_head		container_next;
 	enum vfio_group_type		type;
-	unsigned int			dev_counter;
 	struct rw_semaphore		group_rwsem;
 	struct kvm			*kvm;
 	struct file			*opened_file;
@@ -608,7 +607,6 @@ static int __vfio_register_dev(struct vfio_device *device,
 
 	mutex_lock(&group->device_lock);
 	list_add(&device->group_next, &group->device_list);
-	group->dev_counter++;
 	mutex_unlock(&group->device_lock);
 
 	return 0;
@@ -696,7 +694,6 @@ void vfio_unregister_group_dev(struct vfio_device *device)
 
 	mutex_lock(&group->device_lock);
 	list_del(&device->group_next);
-	group->dev_counter--;
 	mutex_unlock(&group->device_lock);
 
 	if (group->type == VFIO_NO_IOMMU || group->type == VFIO_EMULATED_IOMMU)
@@ -1946,6 +1943,9 @@ EXPORT_SYMBOL(vfio_set_irqs_validate_and_prepare);
  * @prot [in]    : protection flags
  * @pages[out]   : array of host pages
  * Return error or number of pages pinned.
+ *
+ * A driver may only call this function if the vfio_device was created
+ * by vfio_register_emulated_iommu_dev().
  */
 int vfio_pin_pages(struct vfio_device *device, dma_addr_t iova,
 		   int npage, int prot, struct page **pages)
@@ -1961,9 +1961,6 @@ int vfio_pin_pages(struct vfio_device *device, dma_addr_t iova,
 	if (npage > VFIO_PIN_PAGES_MAX_ENTRIES)
 		return -E2BIG;
 
-	if (group->dev_counter > 1)
-		return -EINVAL;
-
 	/* group->container cannot change while a vfio device is open */
 	container = group->container;
 	driver = container->iommu_driver;

base-commit: 568035b01cfb107af8d2e4bd2fb9aea22cf5b868
-- 
2.37.2




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