doc: update recommended IOVA mode for async vhost

DPDK 21.11 adds vfio support for DMA device in vhost. This patch
updates recommended IOVA mode in async datapath.

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index 76f5d303c9df4d352e0decd1b478b4d958efa3e5..7b93116905168dbf0f771518e22955f2ad15954f 100644 (file)
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -442,3 +442,12 @@ Finally, a set of device ops is defined for device specific operations:
 * ``get_notify_area``
 
   Called to get the notify area info of the queue.
+
+Recommended IOVA mode in async datapath
+---------------------------------------
+
+When DMA devices are bound to VFIO driver, VA mode is recommended.
+For PA mode, page by page mapping may exceed IOMMU's max capability,
+better to use 1G guest hugepage.
+
+For UIO driver, any VFIO related error message can be ignored.