[PATCH v4 5/5] vfio: Support IO page table replacement

[Nicolin Chen <nicolinc@nvidia.com>]

Now both the physical path and the emulated path should support an IO page
table replacement.

Call iommufd_device_replace() when vdev->iommufd_attached is true.

Also update the VFIO_DEVICE_ATTACH_IOMMUFD_PT kdoc in the uAPI header.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/vfio/iommufd.c    | 6 +++---
 include/uapi/linux/vfio.h | 6 ++++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/vfio/iommufd.c b/drivers/vfio/iommufd.c
index 8a9457d0a33c..a245a8e0c8ab 100644
--- a/drivers/vfio/iommufd.c
+++ b/drivers/vfio/iommufd.c
@@ -145,9 +145,9 @@ int vfio_iommufd_physical_attach_ioas(struct vfio_device *vdev, u32 *pt_id)
 		return -EINVAL;
 
 	if (vdev->iommufd_attached)
-		return -EBUSY;
-
-	rc = iommufd_device_attach(vdev->iommufd_device, pt_id);
+		rc = iommufd_device_replace(vdev->iommufd_device, pt_id);
+	else
+		rc = iommufd_device_attach(vdev->iommufd_device, pt_id);
 	if (rc)
 		return rc;
 	vdev->iommufd_attached = true;
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 692156a708bb..14375826a25b 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -243,6 +243,12 @@ struct vfio_device_bind_iommufd {
  *
  * Undo by VFIO_DEVICE_DETACH_IOMMUFD_PT or device fd close.
  *
+ * If a vfio device is currently attached to a valid hw_pagetable, without doing
+ * a VFIO_DEVICE_DETACH_IOMMUFD_PT, a second VFIO_DEVICE_ATTACH_IOMMUFD_PT ioctl
+ * passing in another hw_pagetable (hwpt) id is allowed. This action, also known
+ * as a hw_pagetable replacement, will replace the device's currently attached
+ * hw_pagetable with a new hw_pagetable corresponding to the given pt_id.
+ *
  * @argsz:	user filled size of this data.
  * @flags:	must be 0.
  * @pt_id:	Input the target id which can represent an ioas or a hwpt
-- 
2.39.2