[Qemu-devel] VirtIO issues after 83d768b5640946b7da55ce8335509df297e2c7cd

[Brian Rak]

We recently upgraded to qemu 2.8.0, and noticed a bunch of issues with 
various non-linux operating systems.

I was able to bisect this down to 
83d768b5640946b7da55ce8335509df297e2c7cd being the commit that breaks 
things (0687c37c5eeef8580b31cc6e1202d874833ae38a which is immediately 
prior still works ok).

The issue here seems to be that guests stop receiving packets, and this 
only happens with vhost_net enabled.


I've been consistently able to reproduce this with by booting the 
OpenBSD 5.8 ISO ( 
http://mirrors.evowise.com/pub/OpenBSD/5.8/amd64/install58.iso ), and 
pressing 'A' at the first prompt.  It'll attempt to do a DHCP lease, and 
will succeed prior to 83d7.  After that commit, it'll continue to 
transit DHCP requests, but never actually receive the reply.

So far, we've seen this same problem manifest on the following operating 
systems:

* OpenBSD 5.8
* pfSense 2.2.6 (seems to be FreeBSD 10.1 underneath)
* Windows XP
* "9front" (fork of Plan 9)

More modern operating systems did work, including

* Various Linux distributions (CentOS 6+, Ubuntu 12.04+)
* Modern windows distributions (Server 2012)
* OpenBSD 6

I was pointed to this thread - 
https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg04532.html , 
and if I apply that patch network connectivity begins working normally 
again. (I am running under x86-64 btw)