From 59f286c17262bb52a9d396c154fae6ac6d29186e Mon Sep 17 00:00:00 2001
From: Andrija Panic <andrija.panic@gmail.com>
Date: Thu, 6 Aug 2026 01:28:11 +0200
Subject: [PATCH] KVM: default x86 guests to vga video model when none is
 configured

Without an explicit video model (vm.video.hardware agent property or
video.hardware VM detail), CloudStack emits no <video> element and libvirt
defaults x86 guests to cirrus, which is deprecated in QEMU and renders a
blank console on Windows Server 2025 Core guests. Default unconfigured x86
guests to vga with 32 MiB of VRAM instead. Explicit VM details and agent
properties keep precedence; non-x86 guests (aarch64, s390x) are unchanged.

Fixes #13806
---
 .../resource/LibvirtComputingResource.java    | 15 +++++
 .../LibvirtComputingResourceTest.java         | 57 +++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java b/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java
index 4281036d9456..b822fba52d41 100644
--- a/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java
+++ b/plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java
@@ -318,6 +318,8 @@ public class LibvirtComputingResource extends ServerResourceBase implements Serv
     private static final String KVMCLOCK = "kvmclock";
     private static final String HYPERVCLOCK = "hypervclock";
     private static final String WINDOWS = "Windows";
+    private static final String X86_DEFAULT_VIDEO_MODEL = "vga";
+    private static final int X86_DEFAULT_VIDEO_RAM_KIB = 32768;
     private static final String Q35 = "q35";
     private static final String PTY = "pty";
     private static final String VNC = "vnc";
@@ -3330,6 +3332,14 @@ protected VideoDef createVideoDef(VirtualMachineTO vmTO) {
                 videoRam = NumbersUtil.parseInt(value, videoRam);
             }
         }
+        if (StringUtils.isBlank(videoHw) && isGuestX86(vmTO)) {
+            // With no <video> element libvirt defaults x86 guests to cirrus, which is deprecated
+            // in QEMU and renders a blank console on recent Windows guests (e.g. Windows Server 2025 Core)
+            videoHw = X86_DEFAULT_VIDEO_MODEL;
+            if (videoRam == 0) {
+                videoRam = X86_DEFAULT_VIDEO_RAM_KIB;
+            }
+        }
         return new VideoDef(videoHw, videoRam);
     }
 
@@ -3482,6 +3492,11 @@ public boolean isGuestAarch64() {
         return AARCH64.equals(guestCpuArch);
     }
 
+    protected boolean isGuestX86(VirtualMachineTO vmTO) {
+        String arch = guestCpuArch != null ? guestCpuArch : vmTO.getArch();
+        return arch == null || arch.equals("x86_64") || arch.equals("i686");
+    }
+
     private boolean isGuestS390x() {
         return S390X.equals(guestCpuArch);
     }
diff --git a/plugins/hypervisors/kvm/src/test/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResourceTest.java b/plugins/hypervisors/kvm/src/test/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResourceTest.java
index 639f1dc2894c..e3924fdc9236 100644
--- a/plugins/hypervisors/kvm/src/test/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResourceTest.java
+++ b/plugins/hypervisors/kvm/src/test/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResourceTest.java
@@ -712,6 +712,63 @@ public void testCreateVideoDef() {
         assertXpath(domainDoc, "/video/model/@vram", "200");
     }
 
+    @Test
+    public void testCreateVideoDefX86DefaultsToVga() {
+        VirtualMachineTO to = createDefaultVM(false);
+
+        VideoDef videoDef = libvirtComputingResourceSpy.createVideoDef(to);
+        Document domainDoc = parse(videoDef.toString());
+        assertXpath(domainDoc, "/video/model/@type", "vga");
+        assertXpath(domainDoc, "/video/model/@vram", "32768");
+    }
+
+    @Test
+    public void testCreateVideoDefWindowsDefaultsToVga() {
+        VirtualMachineTO to = createDefaultVM(false);
+        to.setOs("Windows Server 2025 (64-bit)");
+
+        VideoDef videoDef = libvirtComputingResourceSpy.createVideoDef(to);
+        Document domainDoc = parse(videoDef.toString());
+        assertXpath(domainDoc, "/video/model/@type", "vga");
+        assertXpath(domainDoc, "/video/model/@vram", "32768");
+    }
+
+    @Test
+    public void testCreateVideoDefExplicitDetailWins() {
+        VirtualMachineTO to = createDefaultVM(false);
+        Map<String, String> details = new HashMap<>();
+        details.put(VmDetailConstants.VIDEO_HARDWARE, "virtio");
+        details.put(VmDetailConstants.VIDEO_RAM, "65536");
+        to.setDetails(details);
+
+        VideoDef videoDef = libvirtComputingResourceSpy.createVideoDef(to);
+        Document domainDoc = parse(videoDef.toString());
+        assertXpath(domainDoc, "/video/model/@type", "virtio");
+        assertXpath(domainDoc, "/video/model/@vram", "65536");
+    }
+
+    @Test
+    public void testCreateVideoDefAgentPropertyWins() {
+        VirtualMachineTO to = createDefaultVM(false);
+        libvirtComputingResourceSpy.videoHw = "qxl";
+        libvirtComputingResourceSpy.videoRam = 65536;
+
+        VideoDef videoDef = libvirtComputingResourceSpy.createVideoDef(to);
+        Document domainDoc = parse(videoDef.toString());
+        assertXpath(domainDoc, "/video/model/@type", "qxl");
+        assertXpath(domainDoc, "/video/model/@vram", "65536");
+    }
+
+    @Test
+    public void testCreateVideoDefAarch64UnconfiguredStaysEmpty() {
+        VirtualMachineTO to = createDefaultVM(false);
+        to.setArch("aarch64");
+        libvirtComputingResourceSpy.guestCpuArch = "aarch64";
+
+        VideoDef videoDef = libvirtComputingResourceSpy.createVideoDef(to);
+        assertEquals("", videoDef.toString());
+    }
+
     @Test
     public void testCreateRngDef() {
         VirtualMachineTO to = createDefaultVM(false);