[Qemu-devel] [PULL 36/37] vhost-net: disable when cross-endian

["Michael S. Tsirkin" <mst@redhat.com>]

From: Greg Kurz <gkurz@linux.vnet.ibm.com>

As of today, vhost assumes guest and host have the same endianness.
This is definitely not compatible with modern PPC64 and ARM that
can change endianness at runtime. Let's disable vhost-net and print
an error message when we detect such a case:

qemu-system-ppc64: vhost-net does not support cross-endian
qemu-system-ppc64: unable to start vhost net: 38: falling back on userspace virtio

This way users can continue to run VMs without changing their setup and
have a chance to know that performance will be impacted.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/net/vhost_net.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
index 7ac7c21..f87c798 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -275,6 +275,19 @@ static void vhost_net_stop_one(struct vhost_net *net,
     vhost_dev_disable_notifiers(&net->dev, dev);
 }
 
+static bool vhost_net_device_endian_ok(VirtIODevice *vdev)
+{
+#ifdef TARGET_IS_BIENDIAN
+#ifdef HOST_WORDS_BIGENDIAN
+    return virtio_is_big_endian(vdev);
+#else
+    return !virtio_is_big_endian(vdev);
+#endif
+#else
+    return true;
+#endif
+}
+
 int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
                     int total_queues)
 {
@@ -283,6 +296,12 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
     int r, i = 0;
 
+    if (!vhost_net_device_endian_ok(dev)) {
+        error_report("vhost-net does not support cross-endian");
+        r = -ENOSYS;
+        goto err;
+    }
+
     if (!k->set_guest_notifiers) {
         error_report("binding does not support guest notifiers");
         r = -ENOSYS;
-- 
MST