Proxmox 8.1.3 VM won’t boot after RAM increase with memory hotplug enabled

[n_pacheco]

Hi everyone,

I’m running into a weird issue with one VM. When memory hotplug is enabled, if I bump the VM RAM to 32 GB and reboot, the guest fails to come up with the error “kernel panic not syncing: system is deadlock”. If I turn hotplug off, I can raise RAM to 32 GB or even 64 GB and the VM boots normally.

Environment:

Proxmox 8.1.3

LVM storage backend

Relevant VM config (trimmed):

 "agent: 1
boot: order=scsi0;ide2;net0
cpu: host
cores: 48
sockets: 2
vcpus: 16
cpulimit: 96
hotplug: disk,network,usb,memory,cpu
machine: q35
memory: 20480
numa: 1
onboot: 1
ostype: l26
scsihw: virtio-scsi-single
scsi0: DATA01:vm-100-disk-0,iothread=1,size=100G
ide2: none,media=cdrom
meta: creation-qemu=8.1.2,ctime=1706066049"

Has anyone seen this and found a fix? Thanks in advance!

Best regards and thank you for any pointers.

 

[pcarone]

Hi,

This looks like memory hotplug behavior inside the guest. Add the following kernel parameter to the guest’s GRUB configuration so newly hot-added memory is brought online automatically:

 "memhp_default_state=online"

After setting that, memory hotplug worked here and the VM was able to boot cleanly with higher RAM sizes (e.g., 64 GB and 128 GB).

Hope this helps!