7.69 Virtual Machines Hang at Boot if Grant Reference Request Too Large

Virtual machines can hang during the boot sequence if the number of grant references exceeds 32,768.

Messages such as the following are written to /var/log/messages:

timestamp localhost kernel: xen_netfront: Initialising Xen virtual ethernet driver
timestamp localhost kernel: xen_netfront: can't alloc rx grant refs
timestamp localhost kernel: net eth7: only created 7 queues

As of Oracle VM Release 3.4.1, the addition of multi-queue support for Xen network and block drivers to increase I/O throughput requires an increased number of grant references and queues.


Grant references relate to the Xen grant table mechanism. See the Xen documentation for more information.

Workaround: Decrease the value of the xen_netback max_queues option in the /etc/modprobe.d/ovs.conf file on Oracle VM Server. The default value is 8. You can decrease this value to 2, for example. After you save the changes to ovs.conf, you must restart Oracle VM Server for them to take effect.

# Limit Xen netback max queue to 8
options xen_netback max_queues=2

Bug 22831141 and 22817043