[PATCH v4] examples/vdpa: support running in nested virtualization environment

[Hao Chen <chenh@yusur.tech>]

When we run dpdk vdpa in the nested virtual machine vm-L1 and ping
test in vm-L2, the ping is not good. The reason for troubleshooting is
that the virtio net in vm-L2 sends control information to the vring,
and the qemu back-end device in vm-L1 cannot obtain correct data
from the vring. This problem is related to the opening of the vIOMMU.

This patch add flag RTE_VHOST_USER_IOMMU_SUPPORT to use vhost vIOMMU
, VIRTIO_F_IOMMU_PLATFORM feature will be negotiated successfully if
virtio iommu is used in a nested virtualization environment.

The configuration is as follows:
The host starts iommu, and the kernel parameter is added with
'intel_iommu=on iommu=pt'.
VM-L1's xml add viommu and virtio device adds iommu='on' ats='on'.
VM-L2's xml enables viommu, and adds  parameters
'intel_iommu=on iommu=pt' to kernel.

Then the ping test in vm-L2 is OK.

Signed-off-by: Hao Chen <chenh@yusur.tech>
---
v4:
*Simplify the patch. Set the flags RTE_VHOST_USER_IOMMU_SUPPORT default.

v3:
*Modify mail title.

v2:
*fprintf all string including the eal one.
*remove exit(1).

 examples/vdpa/main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/examples/vdpa/main.c b/examples/vdpa/main.c
index 4c7e81d7b6..4d3203f3a7 100644
--- a/examples/vdpa/main.c
+++ b/examples/vdpa/main.c
@@ -214,6 +214,8 @@ start_vdpa(struct vdpa_port *vport)
 	if (client_mode)
 		vport->flags |= RTE_VHOST_USER_CLIENT;
 
+	vport->flags |= RTE_VHOST_USER_IOMMU_SUPPORT;
+
 	if (access(socket_path, F_OK) != -1 && !client_mode) {
 		RTE_LOG(ERR, VDPA,
 			"%s exists, please remove it or specify another file and try again.\n",
-- 
2.27.0