[Qemu-devel] Serial: possible hang during intensive interaction over the console

[Andrey Korolyov]

Given 2.1 and isa-serial output, set as ttyS0 for the guest VM with
9600 baud rate.

The test case is quite simple - display as much data as possible over
serial console and do not hang the system. While qemu-1.1 works
perfectly, with complaining for lost interrupts (known bug for used
guest kernel), 2.1 just hangs after some seconds, eating up all
available cpu quota.

Test case is 'while true; dmesg; done' in serial console. I`d like to
ask to consider this bug as very serious as VM going completely
unresponsive in matter of tens of seconds and there are a lot of side
attacks to produce enough number of printk() to the ttyS0 with serial
console being set up and default settings for almost any distro in
such a way that message suppression would not work and VM can be DoSed
by an unprivileged user.