[3.0] Documentation of /dev/mshv for Microsoft Hypervisor with Dom0 Linux Kernel

[ohault]

Currently, this topic it is still too obscure, meanwhile some personal efforts exist like Hyper-V on Linux (yes, this way around) - scholz.ruhr

https://web.archive.org/web/20241206094036/https://scholz.ruhr/blog/hyper-v-on-linux-yes-this-way-around/

It's quite urgent because Kata VM Isolated Containers on AKS for Pod Sandboxing is going to RTM
https://techcommunity.microsoft.com/t5/apps-on-azure-blog/preview-support-for-kata-vm-isolated-containers-on-aks-for-pod/ba-p/3751557

[HemaBontha]

Hi Oliver, is it fair to understand that you are looking for documentation for Linux as root partition on hyper-v ?

[ohault]

Hi @HemaBontha, you are perfectly right!

I will be a key and strategic requirement for AKS on the Edge and many many more.

[ohault]

Does it possible to have an update on this ?
Is it something we can already try from Azure Linux 3.0 dev branch ?

[ohault]

I still have the same question, but some information will eventually shared publicly during this upcoming FOSDEM 2026 session - https://fosdem.org/2026/schedule/event/BFQ8XA-introducing-mshv-accelerator-in-qemu/

[olljanat]

@ohault I investigated those packages a bit which you mentioned in #10996 and asked Grok to explain.

Binary version of HvLoader looks to be also available in https://packages.microsoft.com/azurelinux/3.0/prod/base/x86_64/Packages/h/

I still have the same question, but some information will eventually shared publicly during this upcoming FOSDEM 2026 session - https://fosdem.org/2026/schedule/event/BFQ8XA-introducing-mshv-accelerator-in-qemu/

IMO, most important part was this picture:

So with those you should be able to build bootable disk image and then you just need re-build kernel for your favorite Linux distro with CONFIG_MSHV_ROOT module enabled.

Also note that EULA inside of those RPM packages very clearly says:

1. INSTALLATION AND USE RIGHTS.
a) General. You may download and use the software solely limited to Azure Kubernetes Service images running as part of Azure Kubernetes Service.

Let me know if you get it working. Other why I will look that my self when I have spare time.

EDIT: From file name like “mshv-26100.7436.2511151828.1-1.azl3.x86_64.rpm” we see that Hyper-V is extracted from Windows Server 2025 and last patched most likely in December (minor number is almost same as in this) and if that is the case, we most likely can assume that licensing terms will be same than with Windows version of Hyper-V when/if this becomes available for on-premise customers.

[olljanat]

There seems to be bugs which indicates that Microsoft is mainly using their internal fork of this code but I managed to get Azure Linux booted to root partition in way that /dev/mshv is available.

Instructions in high level:

• Create VM to Hyper-V and enable nested virtualization support with Set-VMProcessor -ExposeVirtualizationExtensions $true -VMName AzureLinux and you need disable secure boot.
• Install Azure Linux by using custom partitioning where /boot/efi size is example 100MB (default 8MB is way too small).
• Install needed RPM packages with commands:

rpm -i hvloader-1.0.1-5.azl3.x86_64.rpm
rpm -i mshv-bootloader-lx-27744.1000.241101-1329.1.x86_64.rpm
rpm -i mshv-27744.1000.2411011329.1-1.azl3.x86_64.rpm
rpm -i kernel-mshv-6.6.100.mshv1-3.azl3.x86_64.rpm

• Generate initramfs and grub config with commands:

rm /etc/dracut.conf.d/00-xen.conf
dracut --kver 6.6.100.mshv1-3.azl3
grub2-mkconfig > /boot/grub2/grub.cfg

• Reboot

You should see something like this as result:

---

I'm also working on to create build script for Ubuntu 25.10 based image which boots to Hyper-V root partition and would include QEMU 10.2.1 (as it also contains mshv accelerator support now). Booting already works in that but /dev/mshv is not available and loading of mshv_root driver fails so clearly there is still some more step missing which Azure Linux does under the hood.

[ohault]

Any updates with the latest release ?

https://github.com/microsoft/azurelinux/blob/3.0/SPECS/kernel-mshv/kernel-mshv.spec

[excelsi]

I have installed now also a Host VM with Azure Linux and then installed all packages including cloud-hypervisor:
sudo tdnf install hvloader mshv kernel-mshv cloud-hypervisor

The next part i will try to get a Windows VM running under Cloud Hypervisor is this guide:
https://github.com/cloud-hypervisor/cloud-hypervisor/blob/main/docs/windows.md