[PATCH v6 09/24] vfio/pci: Only need to check opened devices in the dev_set for hot reset

[Yi Liu <yi.l.liu@intel.com>]

If the affected device is not opened by any user, it is not necessary to
check its ownership as it will not be opened by any user if a user is hot
resetting a device within this dev_set.

Signed-off-by: Yi Liu <yi.l.liu@intel.com>
---
 drivers/vfio/pci/vfio_pci_core.c | 17 +++++++++++++++--
 include/uapi/linux/vfio.h        |  8 ++++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 65bbef562268..f13b093557a9 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -2429,10 +2429,23 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
 
 	list_for_each_entry(cur_vma, &dev_set->device_list, vdev.dev_set_list) {
 		/*
-		 * Test whether all the affected devices are contained by the
+		 * Test whether all the affected devices can be reset by the
+		 * user.  The affected devices may already been opened or not
+		 * yet.
+		 *
+		 * For the devices not opened yet, user can reset them as it
+		 * reason is that the hot reset is done under the protection
+		 * of the dev_set->lock, and device open is also under this
+		 * lock.  During the hot reset, such devices can not be opened
+		 * by other users.
+		 *
+		 * For the devices that have been opened, needs to check the
+		 * ownership.  If the user provides a set of group fds, test
+		 * whether all the opened affected devices are contained by the
 		 * set of groups provided by the user.
 		 */
-		if (!vfio_dev_in_groups(cur_vma, groups)) {
+		if (cur_vma->vdev.open_count &&
+		    !vfio_dev_in_groups(cur_vma, groups)) {
 			ret = -EINVAL;
 			goto err_undo;
 		}
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 0552e8dcf0cb..f96e5689cffc 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -673,6 +673,14 @@ struct vfio_pci_hot_reset_info {
  * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
  *				    struct vfio_pci_hot_reset)
  *
+ * Userspace requests hot reset for the devices it uses.  Due to the
+ * underlying topology, multiple devices can be affected in the reset
+ * while some might be opened by another user.  To avoid interference
+ * the calling user must ensure all affected devices, if opened, are
+ * owned by itself.
+ *
+ * The ownership is proved by an array of group fds.
+ *
  * Return: 0 on success, -errno on failure.
  */
 struct vfio_pci_hot_reset {
-- 
2.34.1