QEMU agent for graceful shutdown of Windows guests under libvirt/qemu-kvm

libvirt sending an ACPI shutdown doesn't always prompt Windows guests to shutdown. That's why there is a QEMU guest agent (which is also handy for freezing/thawing guest file systems.) Installing QEMU guest agent will also cause libvirt to block on shutdown commands until the guest has terminated.

libvirt XML definition required

<channel type='unix'>
<target type='virtio' name='org.qemu.guest_agent.0'/>
<address type='virtio-serial' controller='0' bus='0' port='1'/>
</channel>

You may also have to create /var/lib/libvirt/qemu/channel/target on the KVM host.

mkdir -p /var/lib/libvirt/qemu/channel/target
chown -R libvirt-qemu:kvm /var/lib/libvirt/qemu/channel/target

virtio-win drivers distributed by the Fedora Project contain the guest-agent and required virtioserial drivers for communication between guest and host and can be downloaded as an RPM package called virtio-win.

Once you have the RPM, you can either install it or convert it to a Debian package using alien. The ISO will be installed to /usr/share/virtio-win/virtio-win.iso and can be mounted in the guest.

virsh attach-disk GuestName /usr/share/virtio-win/virtio-win.iso hdc –type cdrom –mode readonly

Once you have restarted the guest with the XML definition changes, you can complete the following steps

  • Install virtioserial driver for PCI Simple Communication Controller under Device Manager, in the vioserial folder
  • Install the guest-agent located under the guest-agent folder for your architecture in the virtio-win ISO

Intel E1G42ET (82576 controller) SR-IOV with Windows 2008 R2 guest

I've followed the Redhat Enterprise Linux 7 Using SR-IOV guide, with the following changes made for Ubuntu 14.04 and the fact that the Intel driver set (PROWinx64) doesn't install the drivers automatically.

Make sure to bring the network link state up before you start the virtual machine, or the network driver will report "Network cable unplugged" permanently. igbvf doesn't want to detach on Linux 3.10 on Ubuntu 14.04, so I have blacklisted the module.

/etc/modprobe.d/blacklist-igbvf.conf

blacklist igbvf

/etc/modprobe.d/igb.conf

options igb max_vfs=7

Download the latest Intel Virtual Function drivers from the Intel site, extract PROWinx64 with your favourite archival program. Then run the following command:

pnputil -a PRO1000\Winx64\NDIS62\v1q62x64.inf

Then you can either go to Device Manager and scan for New hardware changes or restart the virtual machine. Your guest networking should now be working.

New KVM deployment bugs and recommendations (Ubuntu 14.04: qemu 2.0, libvirt 1.2.4, Linux 3.10)

New Linux KVM qemu deployment, running on Ubuntu 14.04 with Linux 3.10 kernel and openvswitch. Hardware setup is 2 SSD in RAID1, and 2 7200RPM HDD in RAID1 using mdadm. bcache is being used as the backing cache for the HDD.

Bugs

  • hv_vapic ("vapic state='on'" in libvirt) causes Windows 2008 R2 and above VMs not to boot if CPU is an Intel IvyBridge or greater (check /sys/module/kvm_intel/parameters/enable_apicv) – Redhat Bugzilla
  • Linux 3.12 or greater (Ubuntu 14.04 ships with 3.13) have issues with virtio-net NIC and TSO (RX and TX checksuming) offloading – TCP sessions can't be established across virtual machines in certain situations (think a virtual machine as a firewall) – Debian Bugreport
  • Windows virtual machines still freeze up/high latency if you use virtio NIC, this is with the latest signed drivers available from the Fedora Project
  • Still have issues with "Russian roulette" of network interfaces with openvswitch – Blog post

Recommendations

Installed Packages

System
apt-get install haveged ntp sysstat irqbalance acpid
Linux KVM, openvswitch, virt-install, virt-top
apt-get install qemu-kvm libvirt-bin virtinst virt-top openvswitch-switch sysfsutils iotop gdisk iftop
bcache
apt-get install python-software-properties
add-apt-repository ppa:g2p/storage && apt-get update && apt-get install bcache-tools

Tuning memory, scheduler I/O subsystems for Linux KVM

Taken from RHEL 6 tuned (virtual-host)

/etc/sysctl.conf
kernel.sched_min_granularity_ns=10000000
kernel.sched_wakeup_granularity_ns=15000000
vm.dirty_ratio=10
vm.dirty_background_ratio=5
vm.swappiness=10

Disable experimental virtio-net zero copy transmit

RHEL 7 has experimental_zcopytx disabled by default.

/etc/modprobe.d/vhost-net.conf
options vhost_net  experimental_zcopytx=0

Use virtio-blk for guests, and enable Multiqueue virtio-net (except Windows)

Linux KVM page describing Multiqueue

libvirt
<devices>
  <interface type='network'>
    <model type='virtio'/>
    <driver name='vhost' queues='4'/>
  </interface>
</devices>

Where number of queues is equal to the number of virtual processors assigned to the virtual machine. Don't forget to enable the vhost_net kernel module, edit /etc/default/qemu-kvm and set VHOST_NET_ENABLED=1.

Make sure to enable Multiqueue support in the guest

ethtool -L eth0 combined 4

Use deadline scheduler, and enable transparent hugepages for KVM

/etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="elevator=deadline transparent_hugepage=always"

Don't forget to run update-grub to make the changes persistent.

For Windows guests, take advantage of Hyper-V enlightments and use e1000 Ethernet adapter

Linux KVM presentation on Hyper-V enlightenment (slightly outdated)

  • hv_vapic (for "supported processors") for Virtual APIC
  • hv_time (aka "hypervclock") for TSC invariant timestamps passed to guest
  • hv_relaxed to prevent BSOD under high load (when a timer can't be serviced when expected)
  • hv_spinlocks let's the guest know when a virtual processor is trying to acquire a lock on the same resource as another processor
libvirt
<features>
  <acpi/>
  <apic/>
  <hyperv>
    <relaxed state='on'/>
    <vapic state='on'/>
    <spinlocks state='on' retries='4096'/>
  </hyperv>
</features>
<clock offset='localtime'>
  <timer name='hypervclock' present='yes'/>
  <timer name='hpet' present='no'/>
</clock>

Build and install longterm Linux 3.10 kernel for stability (and working openvswitch with virtio-net)

apt-get -y install build-essential
cd /usr/local/src
wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.10.44.tar.xz
tar -Jxf linux-3.10.44.tar.xz
cd linux-3.10.44
cp /boot/config-`uname -r` .config
make olddefconfig
make -j`nproc` INSTALL_MOD_STRIP=1 deb-pkg
dpkg -i ../*.deb
apt-mark hold linux-libc-dev

Time keeping is king on FreeBSD – TSC and "how not to have time go backwards in guest"

/etc/sysctl.conf
kern.timecounter.hardware=ACPI-fast
/boot/loader.conf
virtio_load="YES"
virtio_pci_load="YES"
virtio_blk_load="YES"
if_vtnet_load="YES"
virtio_balloon_load="YES"
kern.timecounter.smp_tsc="1"
kern.timecounter.invariant_tsc="1"
libvirt
<clock offset='localtime'>
  <timer name='rtc' tickpolicy='catchup'/>
  <timer name='pit' tickpolicy='delay'/>
  <timer name='hpet' present='no'/>
</clock>

Networking with a gateway not on the local subnet on NetBSD at OVH

NetBSD has a FAQ for networking that outlines how to do Networking with a gateway not on the local subnet, unfortunately the recipe that they provide doesn't actually work "in the real world." The route command they provide does not make the network stack send an ARP who-has for the IP address and requires that you statically set the MAC address of the gateway.

I figured out a work-around for this, based on some insight from people on the NetBSD tech-talk mailing list. This allows you to use NetBSD as a guest operating system on providers such as OVH and Hetzner:

# ifconfig fxp0 inet 10.0.0.1 
# route add -net 192.168.0.1/32 -cloning -link fxp0 -iface 
# route add default -ifa 10.0.0.1 192.168.0.1

The trick was to specify use route cloning, and use a net definition instead of a host definition. Now NetBSD will send an ARP who-has request for the gateway IP address.

To supplement the OVH bridge client guide that is available on their Wiki, it would fit into the following template:

# ifconfig fxp0 inet Fail.over.IP netmask 255.255.255.255 broadcast Fail.over.IP 
# route add -net Your.Server.IP.254/32 -cloning -link fxp0 -iface 
# route add default -ifa Fail.over.IP Your.Server.IP.254

This should allow you to use NetBSD as a guest and not get blocked by OVH robots that check for too many ARP requests.

Accessing USB devices as non-root: writing udev rules the easy way

I recently purchased a TEMPered USB thermometer, which I wanted to use as non-root using an open source utility called TEMPered. All the recipes I found, required that I use root to access the /dev/hidraw0 device that the particular TEMPered USB device exposed – of course this was not acceptable.

systemd (and udev, in general – I believe) has a handy utility called udevadm. You can use this tool to query a device on your system, for example:

udevadm info --query=all --name=/dev/hidraw0 --attribute-walk

Which allows you to retrieve all the required attributes to craft a file to put in /etc/dev/rules.d. I have created the following to expose PCsensor TEMPerV1.4 to a user that is part of the group temper:

# TEMPer1.4 USB thermometer
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="0c45", ATTRS{idProduct}=="7401", GROUP="temper", MODE="0660"

I placed this in a file called /etc/udev/rules.d/60-temper.rules. You can now use TEMPered as a non-root user, which is a member of the group in question!