[dpdk-dev] [PATCH v2 2/3] vhost: add flag to enable iommu support

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Qemu versions from v2.7.0 to v2.9.0 have their reply-ack protocol
feature implementation broken with multiqueue. The reply-ack
protocol feature is optional except for IOMMU feature.

This patch introduce a new RTE_VHOST_USER_IOMMU_SUPPORT flag to
enable VIRTIO_F_IOMMU_PLATFORM virtio feature.

By default, the IOMMU support is now disabled.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 doc/guides/prog_guide/vhost_lib.rst    | 14 ++++++++++++++
 doc/guides/rel_notes/release_17_11.rst |  3 ++-
 lib/librte_vhost/rte_vhost.h           |  1 +
 lib/librte_vhost/socket.c              |  6 ++++++
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
index d02e3cf50..e71bdbd51 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -110,6 +110,20 @@ The following is an overview of some key Vhost API functions:
       of those segments, thus the fewer the segments, the quicker we will get
       the mapping. NOTE: we may speed it by using tree searching in future.
 
+  - ``RTE_VHOST_USER_IOMMU_SUPPORT``
+
+    IOMMU support will be enabled when this flag is set. It is disabled by
+    default.
+
+    Enabling this flag makes possible to use guest vIOMMU to protect vhost
+    from accessing memory the virtio device isn't allowed to, when the feature
+    is negotiated and an IOMMU device is declared.
+
+    However, this feature enables vhost-user's reply-ack protocol feature,
+    which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
+    Enabling this flag with these Qemu version results in Qemu being blocked
+    when multiple queue pairs are declared.
+
 * ``rte_vhost_driver_set_features(path, features)``
 
   This function sets the feature bits the vhost-user driver supports. The
diff --git a/doc/guides/rel_notes/release_17_11.rst b/doc/guides/rel_notes/release_17_11.rst
index b96b23614..06f2a302c 100644
--- a/doc/guides/rel_notes/release_17_11.rst
+++ b/doc/guides/rel_notes/release_17_11.rst
@@ -162,7 +162,8 @@ New Features
 * **Added IOMMU support to libvhost-user**
 
   Implemented device IOTLB in Vhost-user backend, and enabled Virtio's IOMMU
-  feature.
+  feature. The feature is disabled by default, and can be enabled by setting
+  RTE_VHOST_USER_IOMMU_SUPPORT flag at vhost device registration time.
 
 * **Added the Event Ethernet Adapter Library.**
 
diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index fe5c94c69..f65364495 100644
--- a/lib/librte_vhost/rte_vhost.h
+++ b/lib/librte_vhost/rte_vhost.h
@@ -56,6 +56,7 @@ extern "C" {
 #define RTE_VHOST_USER_CLIENT		(1ULL << 0)
 #define RTE_VHOST_USER_NO_RECONNECT	(1ULL << 1)
 #define RTE_VHOST_USER_DEQUEUE_ZERO_COPY	(1ULL << 2)
+#define RTE_VHOST_USER_IOMMU_SUPPORT	(1ULL << 3)
 
 /**
  * Information relating to memory regions including offsets to
diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 701815021..422da002f 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -68,6 +68,7 @@ struct vhost_user_socket {
 	bool is_server;
 	bool reconnect;
 	bool dequeue_zero_copy;
+	bool iommu_support;
 
 	/*
 	 * The "supported_features" indicates the feature bits the
@@ -669,6 +670,11 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 	vsocket->supported_features = VIRTIO_NET_SUPPORTED_FEATURES;
 	vsocket->features           = VIRTIO_NET_SUPPORTED_FEATURES;
 
+	if (!(flags & RTE_VHOST_USER_IOMMU_SUPPORT)) {
+		vsocket->supported_features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
+		vsocket->features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
+	}
+
 	if ((flags & RTE_VHOST_USER_CLIENT) != 0) {
 		vsocket->reconnect = !(flags & RTE_VHOST_USER_NO_RECONNECT);
 		if (vsocket->reconnect && reconn_tid == 0) {
-- 
2.13.6