andrijapanicsb opened a new issue, #13806:
URL: https://github.com/apache/cloudstack/issues/13806
## Summary
On KVM, CloudStack does not specify a video model unless `vm.video.hardware`
(agent
property) or the `video.hardware` VM setting is set. libvirt then falls back
to its
x86 default, **cirrus** — a device QEMU deprecated years ago. With Windows
Server 2025
**Core**, the guest boots fine but the console never renders: `LogonUI.exe`
stays
completely blank (mouse cursor moves, keyboard input incl. Ctrl-Alt-Del is
delivered,
qemu-guest-agent works — only the display output is missing). The VM is
effectively
unusable via the console.
Switching the same VM to `video.hardware=vga` renders the logon UI
immediately.
Reported against 4.22/4.23-era code; the selection logic is unchanged on main
(`LibvirtComputingResource.createVideoDef()`: uses `vm.video.hardware`,
default null →
no `<video>` model emitted → libvirt default cirrus).
## Reproduction (A/B on the same VM)
Environment: EL9 KVM host (qemu-kvm 9.x), CloudStack KVM agent, guest =
Windows Server
2025 Standard Evaluation, **Server Core**, UEFI (OVMF), q35, virtio disk/NIC.
1. Start the VM with no video setting → libvirt gives `<model type='cirrus'
vram='16384'/>`.
- Guest boots (qemu-guest-agent responds, `guest-exec` works, CPU active).
- Console: LogonUI window frame visible, content area entirely black.
Mouse moves,
Ctrl-Alt-Del (sent via console and via `virsh send-key`) is accepted
but nothing
ever paints. (Screenshots available; can attach on request.)
2. Stop the VM, set VM setting `video.hardware=vga` (+ `video.ram=32768`),
start.
- Same boot, console immediately shows `Press Ctrl-Alt-Del to unlock` at
high
resolution. (Screenshot available.)
Data point narrowing the scope: a **Desktop Experience** (full UI) Windows
Server 2025
deployed on the same platform renders on cirrus — the total render failure
appears
specific to **Server Core**'s minimal logon/display stack. (Cirrus is still
limited to
1024x768-ish modes and 16 MB VRAM for every guest.)
## Why cirrus is the wrong default in 2026 (references)
1. **QEMU deprecation warning, emitted live on EL9** when CloudStack starts
such a VM:
`qemu-kvm: warning: 'cirrus-vga' is deprecated, please use a different
VGA card instead`
2. **QEMU switched its own default** away from cirrus to `-vga std` in
**QEMU 2.2 (2014)**
(see QEMU 2.2 changelog).
3. **Gerd Hoffmann (QEMU display maintainer), "qemu: using cirrus considered
harmful"**
(kraxel.org, 2014): 16 MB VRAM ceiling, no modes beyond 1024x768@24bpp,
depends on
ancient guest drivers; recommends stdvga for Windows guests.
4. **Ecosystem defaults**: virt-manager/virt-install (via libosinfo) select
vga/QXL/virtio
for modern guests; Proxmox VE defaults to std VGA; OpenStack Nova moved
its default
video model off cirrus. CloudStack is the outlier by inheriting libvirt's
legacy default.
## Proposal
- Emit an explicit `<video>` model on KVM instead of inheriting libvirt's
cirrus default.
`vga` (standard VBE) is the conservative candidate — every mainstream OS
since ~2005
drives it with inbox drivers; virtio-gpu could be opt-in where guest
drivers exist.
- A default change needs an OS render matrix (Windows 7/10/11, Server
2016-2025 Core and
Desktop, EL7-9, Ubuntu LTS, FreeBSD) — listing it here explicitly so the
scope is clear.
- At minimum until then: document that Windows Server 2025 Core requires
`video.hardware=vga`, and consider defaulting vga for Windows guest-OS
types.
## Workarounds (verified)
- Per VM: settings `video.hardware=vga`, `video.ram=32768` (stopped VM),
then start.
- Per host: agent property `vm.video.hardware=vga` in `agent.properties`.
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