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Windows 10 on Debian under KVM

Here are some things that you need to do to get Windows 10 running on a Debian host under KVM.

UEFI Booting

UEFI is big and complex, but most of what it does isn’t needed at all. If all you want to do is boot from an image of a disk with a GPT partition table then you just install the package ovmf and add something like the following to your KVM start script:

UEFI="-drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_CODE.fd -drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_VARS.fd"

Note that some of the documentation on this doesn’t have the OVMF_VARS.fd file set to readonly. Allowing writes to that file means that the VM boot process (and maybe later) can change EFI variables that affect later boots and other VMs if they all share the same file. For a basic boot you don’t need to change variables so you want it read-only. Also having it read-only is necessary if you want to run KVM as non-root.

As an experiment I tried booting without the OVMF_VARS.fd file, it didn’t boot and then even after configuring it to use the OVMF_VARS.fd file again Windows gave a boot error about the “boot configuration data file” that required booting from recovery media. Apparently configuration mistakes with EFI can mess up the Windows installation, so be careful and backup the Windows installation regularly!

Linux can boot from EFI but you generally don’t want to unless the boot device is larger than 2TB. It’s relatively easy to convert a Linux installation on a GPT disk to a virtual image on a DOS partition table disk or on block devices without partition tables and that gives a faster boot. If the same person runs the host hardware and the VMs then the best choice for Linux is to have no partition tables just one filesystem per block device (which makes resizing much easier) and have the kernel passed as a parameter to kvm. So booting a VM from EFI is probably only useful for booting Windows VMs and for Linux boot loader development and testing.

As an aside, the Debian Wiki page about Secure Boot on a VM [4] was useful for this. It’s unfortunate that it and so much of the documentation about UEFI is about secure boot which isn’t so useful if you just want to boot a system without regard to the secure boot features.

Emulated IDE Disks

Debian kernels (and probably kernels from many other distributions) are compiled with the paravirtualised storage device drivers. Windows by default doesn’t support such devices so you need to emulate an IDE/SATA disk so you can boot Windows and install the paravirtualised storage driver. The following configuration snippet has a commented line for paravirtualised IO (which is fast) and an uncommented line for a virtual IDE/SATA disk that will allow an unmodified Windows 10 installation to boot.

#DRIVE="-drive format=raw,file=/home/kvm/windows10,if=virtio"
DRIVE="-drive id=disk,format=raw,file=/home/kvm/windows10,if=none -device ahci,id=ahci -device ide-drive,drive=disk,bus=ahci.0"

Spice Video

Spice is an alternative to VNC, Here is the main web site for Spice [1]. Spice has many features that could be really useful for some people, like audio, sharing USB devices from the client, and streaming video support. I don’t have a need for those features right now but it’s handy to have options. My main reason for choosing Spice over VNC is that the mouse cursor in the ssvnc doesn’t follow the actual mouse and can be difficult or impossible to click on items near edges of the screen.

The following configuration will make the QEMU code listen with SSL on port 1234 on all IPv4 addresses. Note that this exposes the Spice password to anyone who can run ps on the KVM server, I’ve filed Debian bug #965061 requesting the option of a password file to address this. Also note that the “qxl” virtual video hardware is VGA compatible and can be expected to work with OS images that haven’t been modified for virtualisation, but that they work better with special video drivers.

KEYDIR=/etc/letsencrypt/live/kvm.example.com-0001
-spice password=xxxxxxxx,x509-cacert-file=$KEYDIR/chain.pem,x509-key-file=$KEYDIR/privkey.pem,x509-cert-file=$KEYDIR/cert.pem,tls-port=1234,tls-channel=main -vga qxl

To connect to the Spice server I installed the spice-client-gtk package in Debian and ran the following command:

spicy -h kvm.example.com -s 1234 -w xxxxxxxx

Note that this exposes the Spice password to anyone who can run ps on the system used as a client for Spice, I’ve filed Debian bug #965060 requesting the option of a password file to address this.

This configuration with an unmodified Windows 10 image only supported 800*600 resolution VGA display.

Networking

To set up bridged networking as non-root you need to do something like the following as root:

chgrp kvm /usr/lib/qemu/qemu-bridge-helper
setcap cap_net_admin+ep /usr/lib/qemu/qemu-bridge-helper
mkdir -p /etc/qemu
echo "allow all" > /etc/qemu/bridge.conf
chgrp kvm /etc/qemu/bridge.conf
chmod 640 /etc/qemu/bridge.conf

Windows 10 supports the emulated Intel E1000 network card. Configuration like the following configures networking on a bridge named br0 with an emulated E1000 card. MAC addresses that have a 1 in the second least significant bit of the first octet are “locally administered” (like IPv4 addresses starting with “10.”), see the Wikipedia page about MAC Address for details.

The following is an example of network configuration where $ID is an ID number for the virtual machine. So far I haven’t come close to 256 VMs on one network so I’ve only needed one octet.

NET="-device e1000,netdev=net0,mac=02:00:00:00:01:$ID -netdev tap,id=net0,helper=/usr/lib/qemu/qemu-bridge-helper,br=br0"

Final KVM Settings

KEYDIR=/etc/letsencrypt/live/kvm.example.com-0001
SPICE="-spice password=xxxxxxxx,x509-cacert-file=$KEYDIR/chain.pem,x509-key-file=$KEYDIR/privkey.pem,x509-cert-file=$KEYDIR/cert.pem,tls-port=1234,tls-channel=main -vga qxl"

UEFI="-drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_CODE.fd -drive if=pflash,format=raw,readonly,file=/usr/share/OVMF/OVMF_VARS.fd"

DRIVE="-drive format=raw,file=/home/kvm/windows10,if=virtio"

NET="-device e1000,netdev=net0,mac=02:00:00:00:01:$ID -netdev tap,id=net0,helper=/usr/lib/qemu/qemu-bridge-helper,br=br0"

kvm -m 4000 -smp 2 $SPICE $UEFI $DRIVE $NET

Windows Settings

The Spice Download page has a link for “spice-guest-tools” that has the QNX video driver among other things [2]. This seems to be needed for resolutions greater than 800*600.

The Virt-Manager Download page has a link for “virt-viewer” which is the Spice client for Windows systems [3], they have MSI files for both i386 and AMD64 Windows.

It’s probably a good idea to set display and system to sleep after never (I haven’t tested what happens if you don’t do that, but there’s no benefit in sleeping). Before uploading an image I disabled the pagefile and set the partition to the minimum size so I had less data to upload.

Problems

Here are some things I haven’t solved yet.

The aSpice Android client for the Spice protocol fails to connect with the QEMU code at the server giving the following message on stderr: “error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca:../ssl/record/rec_layer_s3.c:1544:SSL alert number 48“.

Spice is supposed to support dynamic changes to screen resolution on the VM to match the window size at the client, this doesn’t work for me, not even with the Red Hat QNX drivers installed.

The Windows Spice client doesn’t seem to support TLS, I guess running some sort of proxy for TLS would work but I haven’t tried that yet.

6 comments to Windows 10 on Debian under KVM

  • anonymous

    I’ve had wonderful success with gnome-boxes, which has a built-in spice client.

  • Timo Lindfors

    You can use virt-viewer on Windows to get TLS working with spice. If you configure Firefox with network.protocol-handler.expose.spice=false you can configure Firefox to use remote-viewer.exe for handling spice URLs.

  • Timo Lindfors

    Dynamic changes to the resolution require some support from the guest OS afaik. If you use e.g. xfce4 it does not seem to work. For me it works with gnome3.

  • Paul Menzel

    Thank you for the article. I noticed some small things:

    1. The first code line misses an = after UEFI.
    2. The note about the spice password is twice in the text.
    3. to setup → to set up

  • https://wiki.gnome.org/Apps/Boxes
    Thanks anon, Gnome Boxes looks like an interesting project. Not a good fit for my needs (as they say on their Wiki) but good for regular desktop use.

    Timo how exactly do you get TLS going on Windows? virt-viewer doesn’t seem to have an option for it, but the changelog mentions TLS support so I guess I missed something and I’ll try it again.

    It’s great that GNOME3 supports dynamic resolution changes. But not useful for me as I don’t have a Linux desktop install on any VM as I can configure all Linux stuff from the command line. What I want to do is get a Windows desktop going well because Windows is pretty much unusable without a GUI.

    Paul: 1 and 3 Thanks fixed that. 2 I have separate mentions of the client and server issues, maybe not described as clearly as it could be but doesn’t seem to be duplicated.

  • Timo Lindfors

    Afaik TLS worked simply by using a spice:// URL with tls-port parameter set.

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