[ovs-dev] [RFC PATCH V2 2/2] netdev-dpdk: add support for vhost IOMMU feature

Mark Kavanagh mark.b.kavanagh at intel.com
Wed Nov 8 12:00:10 UTC 2017


DPDK v17.11 introduces support for the vHost IOMMU feature.
This is a security feature, that 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 vhost port option, vhost-iommu-support,
to allow enablement of the vhost IOMMU feature:

    $ ovs-vsctl add-port br0 vhost-client-1 \
        -- set Interface vhost-client-1 type=dpdkvhostuserclient \
             options:vhost-server-path=$VHOST_USER_SOCKET_PATH   \
             options:vhost-iommu-support=true

Note that support for this feature is only implemented for vhost
user client ports (since vhost user ports are considered deprecated).

Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
---
 Documentation/topics/dpdk/vhost-user.rst | 21 +++++++++++++++++++++
 NEWS                                     |  1 +
 lib/netdev-dpdk.c                        | 29 ++++++++++++++++++++++++++---
 vswitchd/vswitch.xml                     | 10 ++++++++++
 4 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst
index fdf6ae1..6d65971 100644
--- a/Documentation/topics/dpdk/vhost-user.rst
+++ b/Documentation/topics/dpdk/vhost-user.rst
@@ -250,6 +250,27 @@ Once the vhost-user-client ports have been added to the switch, they must be
 added to the guest. Like vhost-user ports, there are two ways to do this: using
 QEMU directly, or using libvirt. Only the QEMU case is covered here.
 
+vhost-user client IOMMU
+~~~~~~~~~~~~~~~~~~~~~~~
+It is possible to enable IOMMU support for vHost User client ports. This is
+a feature which restricts the vhost memory that a virtio device can access, and
+as such is useful in deployments in which security is a concern. IOMMU mode may
+be enabled on the command line::
+
+    $ ovs-vsctl add-port br0 vhost-client-1 \
+        -- set Interface vhost-client-1 type=dpdkvhostuserclient \
+             options:vhost-server-path=$VHOST_USER_SOCKET_PATH   \
+             options:vhost-iommu-support=true
+
+.. important::
+
+    Enabling the IOMMU feature also enables the vhost user reply-ack protocol;
+    this is known to work on QEMU v2.10.0, but is buggy on older versions
+    (2.7.0 - 2.9.0, inclusive). Consequently, the IOMMU feaure is disabled by
+    default (and should remain so if using the aforementioned versions of QEMU).
+    Starting with QEMU v2.9.1, vhost-iommu-support can safely be enabled, even
+    without having an IOMMU device, with no performance penalty.
+
 Adding vhost-user-client ports to the guest (QEMU)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/NEWS b/NEWS
index 6acd8bd..de53d2f 100644
--- a/NEWS
+++ b/NEWS
@@ -13,6 +13,7 @@ Post-v2.8.0
      * Add support for compiling OVS with the latest Linux 4.13 kernel
    - DPDK:
      * Add support for DPDK v17.11
+     * Add support for vHost IOMMU feature
 
 v2.8.0 - 31 Aug 2017
 --------------------
diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
index ed5bf62..2e9633a 100644
--- a/lib/netdev-dpdk.c
+++ b/lib/netdev-dpdk.c
@@ -1424,15 +1424,29 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev,
 {
     struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
     const char *path;
+    bool iommu_enable;
+    bool request_reconfigure = false;
+    uint64_t vhost_driver_flags_prev = dev->vhost_driver_flags;
 
     ovs_mutex_lock(&dev->mutex);
     if (!(dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT)) {
         path = smap_get(args, "vhost-server-path");
         if (path && strcmp(path, dev->vhost_id)) {
             strcpy(dev->vhost_id, path);
-            netdev_request_reconfigure(netdev);
+            request_reconfigure = true;
         }
     }
+
+    iommu_enable = smap_get_bool(args, "vhost-iommu-support", false);
+    if (iommu_enable)
+        dev->vhost_driver_flags |= RTE_VHOST_USER_IOMMU_SUPPORT;
+    else
+        dev->vhost_driver_flags &= ~RTE_VHOST_USER_IOMMU_SUPPORT;
+    if (vhost_driver_flags_prev != dev->vhost_driver_flags)
+        request_reconfigure = true;
+
+    if (request_reconfigure)
+        netdev_request_reconfigure(netdev);
     ovs_mutex_unlock(&dev->mutex);
 
     return 0;
@@ -3326,9 +3340,18 @@ netdev_dpdk_vhost_client_reconfigure(struct netdev *netdev)
      */
     if (!(dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT)
             && strlen(dev->vhost_id)) {
+        /* Enable vhost IOMMU, if it was requested.
+         * XXX: the 'flags' variable is required, as not all vhost backend
+         * features are currently supported by OvS; in time, it should be
+         * possible to invoke rte_vhost_driver_register(), passing
+         * dev->vhost_driver_flags directly as a parameter to same.
+         */
+        uint64_t flags = RTE_VHOST_USER_CLIENT;
+        if (dev->vhost_driver_flags & RTE_VHOST_USER_IOMMU_SUPPORT)
+            flags |= RTE_VHOST_USER_IOMMU_SUPPORT;
+
         /* Register client-mode device */
-        err = rte_vhost_driver_register(dev->vhost_id,
-                                        RTE_VHOST_USER_CLIENT);
+        err = rte_vhost_driver_register(dev->vhost_id, flags);
         if (err) {
             VLOG_ERR("vhost-user device setup failure for device %s\n",
                      dev->vhost_id);
diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index c145e1a..a633226 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -2654,6 +2654,16 @@ ovs-vsctl add-port br0 p0 -- set Interface p0 type=patch options:peer=p1 \
         </p>
       </column>
 
+      <column name="options" key="vhost-iommu-support"
+              type='{"type": "boolean"}'>
+        <p>
+          The value specifies whether IOMMU support is enabled for a vHost User
+          client mode device that has been or will be created by QEMU.
+          Only supported by dpdkvhostuserclient interfaces. If not specified or
+          an incorrect value is specified, defaults to 'false'.
+        </p>
+      </column>
+
       <column name="options" key="n_rxq_desc"
               type='{"type": "integer", "minInteger": 1, "maxInteger": 4096}'>
         <p>
-- 
1.9.3



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