virtio_net: Bypass backends for MTU feature negotiation

This patch adds a new internal "x-mtu-bypass-backend" property
to bypass backends for MTU feature negotiation.

When this property is set, the MTU feature is negotiated as soon
as supported by the guest and a MTU value is set via the host_mtu
parameter. In case the backend advertises the feature (e.g. DPDK's
vhost-user backend), the feature negotiation is propagated down to
the backend.

When this property is not set, the backend has to support the MTU
feature for its negotiation to succeed.

For compatibility purpose, this property is disabled for machine
types v2.9 and older.

Cc: Aaron Conole <aconole@redhat.com>
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Vlad Yasevich <vyasevic@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 98bd683f31b51892877a3118a5df54dd99d67118..9a3d769aa2ae5af8d1554816a7a5397f70e3524f 100644 (file)
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -589,7 +589,15 @@ static uint64_t virtio_net_get_features(VirtIODevice *vdev, uint64_t features,
     if (!get_vhost_net(nc->peer)) {
         return features;
     }
-    return vhost_net_get_features(get_vhost_net(nc->peer), features);
+    features = vhost_net_get_features(get_vhost_net(nc->peer), features);
+    vdev->backend_features = features;
+
+    if (n->mtu_bypass_backend &&
+            (n->host_features & 1ULL << VIRTIO_NET_F_MTU)) {
+        features |= (1ULL << VIRTIO_NET_F_MTU);
+    }
+
+    return features;
 }
 
 static uint64_t virtio_net_bad_features(VirtIODevice *vdev)
@@ -640,6 +648,11 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features)
     VirtIONet *n = VIRTIO_NET(vdev);
     int i;
 
+    if (n->mtu_bypass_backend &&
+            !virtio_has_feature(vdev->backend_features, VIRTIO_NET_F_MTU)) {
+        features &= ~(1ULL << VIRTIO_NET_F_MTU);
+    }
+
     virtio_net_set_multiqueue(n,
                               virtio_has_feature(features, VIRTIO_NET_F_MQ));
 
@@ -2093,6 +2106,8 @@ static Property virtio_net_properties[] = {
     DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size,
                        VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE),
     DEFINE_PROP_UINT16("host_mtu", VirtIONet, net_conf.mtu, 0),
+    DEFINE_PROP_BOOL("x-mtu-bypass-backend", VirtIONet, mtu_bypass_backend,
+                     true),
     DEFINE_PROP_END_OF_LIST(),
 };
 

diff --git a/include/hw/compat.h b/include/hw/compat.h
index 4c53d600c1c3a55509b2ab8ac9e1a64964205670..400c64b3183638b6666b4e6fcf872bb140fcb732 100644 (file)
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -10,6 +10,10 @@
         .driver   = "intel-iommu",\
         .property = "pt",\
         .value    = "off",\
+    },{\
+        .driver   = "virtio-net-device",\
+        .property = "x-mtu-bypass-backend",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_8 \

diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 1eec9a2da3b697f48e1963db448e2f00f74814dd..602b4868d4007bb9d93a45611a736273ef2467df 100644 (file)
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -97,6 +97,7 @@ typedef struct VirtIONet {
     QEMUTimer *announce_timer;
     int announce_counter;
     bool needs_vnet_hdr_swap;
+    bool mtu_bypass_backend;
 } VirtIONet;
 
 void virtio_net_set_netclient_name(VirtIONet *n, const char *name,

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 7b6edbafd7141c3b4e73a28bd61f5323d87c5f1d..80c45c321e2cc26de2cfc18a7942aa6495dadaf9 100644 (file)
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -79,6 +79,7 @@ struct VirtIODevice
     uint16_t queue_sel;
     uint64_t guest_features;
     uint64_t host_features;
+    uint64_t backend_features;
     size_t config_len;
     void *config;
     uint16_t config_vector;