netdev-dpdk: vHost IOMMU support

DPDK v17.11 introduces support for the vHost IOMMU feature.
This is a security feature, which restricts the vhost memory
that a virtio device may access.

This feature also enables the vhost REPLY_ACK protocol, the
implementation of which is known to work in newer versions of
QEMU (i.e. v2.10.0), but is buggy in older versions (v2.7.0 -
v2.9.0, inclusive). As such, the feature is disabled by default
in (and should remain so), for the aforementioned older QEMU
verions. Starting with QEMU v2.9.1, vhost-iommu-support can
safely be enabled, even without having an IOMMU device, with
no performance penalty.

This patch adds a new global config option, vhost-iommu-support,
that controls enablement of the vhost IOMMU feature:

    ovs-vsctl set Open_vSwitch . other_config:vhost-iommu-support=true

This value defaults to false; to enable IOMMU support, this field
should be set to true when setting other global parameters on init
(such as "dpdk-socket-mem", for example). Changing the value at
runtime is not supported, and requires restarting the vswitch daemon.

Signed-off-by: Mark Kavanagh <mark.b.kavanagh@intel.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/dpdk.c

@@ -41,6 +41,7 @@ VLOG_DEFINE_THIS_MODULE(dpdk);
 static FILE *log_stream = NULL;       /* Stream for DPDK log redirection */
 
 static char *vhost_sock_dir = NULL;   /* Location of vhost-user sockets */
+static bool vhost_iommu_enabled = false; /* Status of vHost IOMMU support */
 
 static int
 process_vhost_flags(char *flag, const char *default_val, int size,
@@ -345,6 +346,11 @@ dpdk_init__(const struct smap *ovs_other_config)
         vhost_sock_dir = sock_dir_subcomponent;
     }
 
+    vhost_iommu_enabled = smap_get_bool(ovs_other_config,
+                                        "vhost-iommu-support", false);
+    VLOG_INFO("IOMMU support for vhost-user-client %s.",
+               vhost_iommu_enabled ? "enabled" : "disabled");
+
     argv = grow_argv(&argv, 0, 1);
     argc = 1;
     argv[0] = xstrdup(ovs_get_program_name());
@@ -482,6 +488,12 @@ dpdk_get_vhost_sock_dir(void)
     return vhost_sock_dir;
 }
 
+bool
+dpdk_vhost_iommu_enabled(void)
+{
+    return vhost_iommu_enabled;
+}
+
 void
 dpdk_set_lcore_id(unsigned cpu)
 {