Display serial0 with i440fx and virtiofs does not boot

[leesteken]

A VM with Machine Default (i440fx) and a Virtiofs cannot boot with Display Serial terminal 0 (serial0): it only shows 1 vCPU 100% endlessly without any serial terminal output.

It boots fine without a virtiofs or with a different display or using q35, My work-around for my headless Ubuntu Server 26.04 is using q35 instead. The system log shows these errors:

pvedaemon[314754]: <root@pam> starting task UPID:sentry:0005C709:0038024D:6AD258A3:qmstop:117:root@pam:
pvedaemon[314754]: worker exit
QEMU[378005]: kvm: Failed to read msg header. Read 0 instead of 12. Original request 0.
QEMU[378005]: kvm: Failed to set msg fds.
QEMU[378005]: kvm: vhost VQ 1 ring restore failed: -22: Invalid argument (22)
QEMU[378005]: kvm: Failed to set msg fds.
QEMU[378005]: kvm: vhost_set_vring_call failed 22
QEMU[378005]: kvm: Failed to set msg fds.
QEMU[378005]: kvm: vhost_set_vring_call failed 22
unknown[377999]: sentry virtiofsd[377997]: Waiting for daemon failed: WaitDaemon(Any { .. })
unknown[377999]: sentry virtiofsd[377997]: Error in vring worker: Any { .. }
pvedaemon[2499]: worker 314754 finished

EDIT: Up to date no-subscription PVE 9.2.21.

 

[leesteken]

Another funny thing about this VM configuration is that the Host memory usage is unexpectedly way below the Memory usage:


The entire VM config with the q35 work-around:

agent: 1
args: -boot menu=off -global scsi-hd.physical_block_size=16k -global scsi-hd.logical_block_size=4k
balloon: 2048
bios: ovmf
boot: order=scsi0;scsi1
cores: 2
cpu: custom-Zen3,flags=-nested-virt
cpuunits: 200
efidisk0: qpool:117/vm-117-disk-2.raw,efitype=4m,size=528K
hookscript: local:snippets/mythtv.sh
hotplug: usb
machine: q35
memory: 3072
meta: creation-qemu=11.0.3,ctime=1791910067
name: mythtv
net0: virtio=52:54:56:17:05:17,bridge=vmbr0,firewall=1
net1: virtio=52:54:56:17:03:17,bridge=vmbr3,firewall=1
numa: 0
onboot: 1
ostype: l26
protection: 1
reboot: 0
rng0: source=/dev/urandom
scsi0: none,media=cdrom
scsi1: qpool:117/vm-117-disk-0.raw,cache=writethrough,discard=on,iothread=1,size=8G,ssd=1
scsihw: virtio-scsi-single
serial0: socket
smbios1: uuid=0ae17323-6b09-4030-a3c0-b02fd032d8c2
sockets: 1
spice_enhancements: videostreaming=filter
startup: order=1,down=30
tablet: 0
vga: serial0
virtiofs0: mythtv,cache=never
vmgenid: 32646c27-3ba6-4aca-936b-00973f46dbb4

EDIT: PVE host is not under memory pressure (<35%) and KSM is therefore not active.