[PATCH] example: vdpa: support run 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 NG. 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 option '--iommu-support' to use guest vIOMMU to
protect vhost, then the ping test in vm-L2 is OK.
This option is required in a nested virtualization environment.

Signed-off-by: Hao Chen <chenh@yusur.tech>
---
 examples/vdpa/main.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/examples/vdpa/main.c b/examples/vdpa/main.c
index 4c7e81d7b6..a24c78d7a4 100644
--- a/examples/vdpa/main.c
+++ b/examples/vdpa/main.c
@@ -43,16 +43,20 @@ static char iface[MAX_PATH_LEN];
 static int devcnt;
 static int interactive;
 static int client_mode;
+static int iommu_support;
 
 /* display usage */
 static void
 vdpa_usage(const char *prgname)
 {
-	printf("Usage: %s [EAL options] -- "
-				 "	--interactive|-i: run in interactive mode.\n"
-				 "	--iface <path>: specify the path prefix of the socket files, e.g. /tmp/vhost-user-.\n"
-				 "	--client: register a vhost-user socket as client mode.\n",
-				 prgname);
+	printf("Usage: %s [EAL options] --\n", prgname);
+	const char *usage_str = "	--interactive|-i: run in interactive mode.\n"
+				"	--iface <path>: specify the path prefix of the socket files, e.g. /tmp/vhost-user-.\n"
+				"	--client: register a vhost-user socket as client mode.\n"
+				"	--iommu-support: use guest vIOMMU to protect vhost.\n";
+
+	fprintf(stderr, "%s", usage_str);
+	exit(1);
 }
 
 static int
@@ -63,6 +67,7 @@ parse_args(int argc, char **argv)
 		{"iface", required_argument, NULL, 0},
 		{"interactive", no_argument, &interactive, 1},
 		{"client", no_argument, &client_mode, 1},
+		{"iommu-support", no_argument, &iommu_support, 1},
 		{NULL, 0, 0, 0},
 	};
 	int opt, idx;
@@ -220,6 +225,10 @@ start_vdpa(struct vdpa_port *vport)
 			socket_path);
 		return -1;
 	}
+
+	if (iommu_support)
+		vport->flags |= RTE_VHOST_USER_IOMMU_SUPPORT;
+
 	ret = rte_vhost_driver_register(socket_path, vport->flags);
 	if (ret != 0)
 		rte_exit(EXIT_FAILURE,
-- 
2.27.0