[PATCH qemu-server 2/2] cpu config: disable APICv for Windows 11/2022/2025 to mitigate issues with VBS

[Fiona Ebner <f.ebner@proxmox.com>]

As reported in the community forum [0] and enterprise support, Windows
with MBEC and VBS can have issues on certain Intel CPUs, leading to
guest freezes and 100% CPU usage. The detection/enabling of APICv
support in Windows was determined to be related. Disabling
vmx-apicv-vid and/or vmx-apicv-register mitigates the issue. Disable
both flags starting with a bumped 11.0+pve2 machine version for
consistency.

[0]: https://forum.proxmox.com/threads/184178

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 src/PVE/QemuServer/CPUConfig.pm               | 13 ++++++++++
 src/PVE/QemuServer/Machine.pm                 |  3 ++-
 src/test/cfg2cmd/win11-host-11.0+pve2.conf    |  4 +++
 .../cfg2cmd/win11-host-11.0+pve2.conf.cmd     | 26 +++++++++++++++++++
 4 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 src/test/cfg2cmd/win11-host-11.0+pve2.conf
 create mode 100644 src/test/cfg2cmd/win11-host-11.0+pve2.conf.cmd

diff --git a/src/PVE/QemuServer/CPUConfig.pm b/src/PVE/QemuServer/CPUConfig.pm
index 4f409528..65234489 100644
--- a/src/PVE/QemuServer/CPUConfig.pm
+++ b/src/PVE/QemuServer/CPUConfig.pm
@@ -1055,6 +1055,19 @@ sub get_pve_cpu_flags(
         };
     }
 
+    # Note that this is only relevant for Intel CPUs if nested-virt/vmx is enabled. Otherwise, the
+    # flags are already disabled.
+    if ($arch eq 'x86_64' && $winversion >= 11 && $version_guard->(11, 0, 2)) {
+        $pve_flags->{'vmx-apicv-register'} = {
+            op => '-',
+            reason => "$pve_msg to avoid issues with certain Windows configurations like VBS",
+        };
+        $pve_flags->{'vmx-apicv-vid'} = {
+            op => '-',
+            reason => "$pve_msg to avoid issues with certain Windows configurations like VBS",
+        };
+    }
+
     return $pve_flags;
 }
 
diff --git a/src/PVE/QemuServer/Machine.pm b/src/PVE/QemuServer/Machine.pm
index 37b272c6..04e63f56 100644
--- a/src/PVE/QemuServer/Machine.pm
+++ b/src/PVE/QemuServer/Machine.pm
@@ -44,9 +44,10 @@ our $PVE_MACHINE_VERSION = {
         },
     },
     '11.0' => {
-        highest => 1,
+        highest => 2,
         revisions => {
             '+pve1' => 'Use host_tunnel=off by default for VirtIO NICs.',
+            '+pve2' => 'Disable APICv for Windows 11/2022/2025 to mitigate issues with VBS.',
         },
     },
 };
diff --git a/src/test/cfg2cmd/win11-host-11.0+pve2.conf b/src/test/cfg2cmd/win11-host-11.0+pve2.conf
new file mode 100644
index 00000000..f71e37dd
--- /dev/null
+++ b/src/test/cfg2cmd/win11-host-11.0+pve2.conf
@@ -0,0 +1,4 @@
+# TEST: Simple test for Windows 11 VM with host CPU and machine version 11.0+pve2
+cpu: host
+machine: pc-q35-11.0+pve2
+ostype: win11
diff --git a/src/test/cfg2cmd/win11-host-11.0+pve2.conf.cmd b/src/test/cfg2cmd/win11-host-11.0+pve2.conf.cmd
new file mode 100644
index 00000000..a17d6ffd
--- /dev/null
+++ b/src/test/cfg2cmd/win11-host-11.0+pve2.conf.cmd
@@ -0,0 +1,26 @@
+/usr/bin/kvm \
+  -id 8006 \
+  -name vm8006 \
+  -no-shutdown \
+  -chardev 'socket,id=qmp,path=/var/run/qemu-server/8006.qmp,server=on,wait=off' \
+  -mon 'chardev=qmp,mode=control' \
+  -chardev 'socket,id=qmp-event,path=/var/run/qmeventd.sock,reconnect-ms=5000' \
+  -mon 'chardev=qmp-event,mode=control' \
+  -pidfile /var/run/qemu-server/8006.pid \
+  -daemonize \
+  -smp '1,sockets=1,cores=1,maxcpus=1' \
+  -nodefaults \
+  -boot 'menu=on,strict=on,reboot-timeout=1000,splash=/usr/share/qemu-server/bootsplash.jpg' \
+  -vnc 'unix:/var/run/qemu-server/8006.vnc,password=on' \
+  -global 'kvm-pit.lost_tick_policy=discard' \
+  -cpu 'host,-cet-ibt,-cet-ss,hv_ipi,hv_relaxed,hv_reset,hv_runtime,hv_spinlocks=0x1fff,hv_stimer,hv_synic,hv_time,hv_vapic,hv_vpindex,+kvm_pv_eoi,+kvm_pv_unhalt,-vmx-apicv-register,-vmx-apicv-vid' \
+  -m 512 \
+  -global 'ICH9-LPC.disable_s3=1' \
+  -global 'ICH9-LPC.disable_s4=1' \
+  -readconfig /usr/share/qemu-server/pve-q35-4.0.cfg \
+  -device 'usb-tablet,id=tablet,bus=ehci.0,port=1' \
+  -device 'VGA,id=vga,bus=pcie.0,addr=0x1,edid=off' \
+  -device 'virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3,free-page-reporting=on' \
+  -iscsi 'initiator-name=iqn.1993-08.org.debian:01:aabbccddeeff' \
+  -rtc 'driftfix=slew,base=localtime' \
+  -machine 'hpet=off,type=pc-q35-11.0+pve2'
-- 
2.47.3