[libvirt] Virtqueue size exceeded error when resuming VM

[Moshe Levi]

Hi,
A new security fix [1],[2] and [3] merged to qemu. 
After updating the packages we started to get "qemu-system-x86_64: Virtqueue size exceeded", when resuming the guest. 

Our environment is OpenStack master and we have Mellanox CI that test SR-IOV functionality.
Ubuntu 14.04 with Qemu 2.0.0+dfsg-2ubuntu1.26 that contains the fixes see [2]
ii  qemu-kvm                            2.0.0+dfsg-2ubuntu1.26                  amd64        QEMU Full virtualization
ii  qemu-system-x86                     2.0.0+dfsg-2ubuntu1.26                  amd64        QEMU full system emulation binaries (x86)
ii  qemu-utils                          2.0.0+dfsg-2ubuntu1.26                  amd64        QEMU utilities
Our CI started to fail last week when this security packages released. 

The scenarios is  as follows (sorry for the OpenStack commands :)) :
1. nova boot guest
2. nova suspend guest
3. nova resume guest

The result is that the guest is in poweroff state and when I power it on everything is working fine.

I tested in direct port (SR-IOV) and normal port (virtual port) and it happens in both cases. 


According to the [3] it prevent from malicious guest to submit more requests than the virtqueuesize permits.
Our CI uses proprietary Cirros image with mlnx4_en driver.  (http://13.69.151.247/images/mellanox_eth.img) 
I started to test it with other images to see if the problem with our image. 
I also tested with Ubuntu image - https://cloud-images.ubuntu.com/wily/current/wily-server-cloudimg-amd64-disk1.img
And OpenStack Cirros image http://download.cirros-cloud.net/0.3.4/cirros-0.3.4-x86_64-disk.img

The Ubuntu image had the same failure, but the  Cirros worked.

I wonder if there is a problem with the patch or with the images? 
What in these images can make them malicious guest? 



[1] - https://access.redhat.com/security/cve/cve-2016-5403
[2] - http://www.ubuntu.com/usn/usn-3047-1/
[3] - https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg06257.html