VMs freeze (kvm ~1100% CPU, split_lock_detect traps) on kernel 7.0.6-2-pve — stable on 7.0.2 base — i9-14900K / ASRock Rack Z690D4U

T

topkung1

Member
Jul 7, 2022
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Hi all,

After the kernel moved from the 7.0.2 base to 7.0.6-2-pve, my Windows VMs
intermittently freeze and only a hard reset recovers them. The 7.0.2 base
(the PVE 9.2 default) has been stable. I am currently pinned back to
7.0.2-7-pve and observing.

Symptoms
- A VM becomes completely unresponsive: RDP disconnects, the noVNC console
shows only a black screen, and the qemu-guest-agent guest-ping times out.
- On the host, the kvm process for the affected VM is pegged at ~1100% CPU
(compute-bound, not I/O wait). Host RAM is healthy (plenty free, swap unused).
- dmesg is full of "x86/split lock detection: #AC ... took a split_lock trap"
messages — some at user-space addresses (0x7ff7...), some in the guest
kernel (0xfffff80...).
- It has happened on two VMs with very different configs (one q35 + OVMF,
the other i440fx + SeaBIOS), so it doesn't look VM-config specific. One of
them was only running a web browser when it froze.
- Only `qm reset` / `qm stop` recovers it.

Host
- CPU: Intel Core i9-14900K (single socket)
- RAM: 64 GB, non-ECC
- Motherboard: ASRock Rack Z690D4U, BIOS 21.12 (2025-11-28)
- Storage: NVMe + SATA SSD
- intel-microcode: 3.20251111.1~deb13u1 (recent — so this is not stale microcode)
- PVE: proxmox-ve 9.2.0, pve-manager 9.2.3, pve-qemu-kvm 11.0.0-4
- Affected kernel: 7.0.6-2-pve | Stable kernel: 7.0.2-7-pve (also 7.0.2-6)

What I've tried
- `sysctl kernel.split_lock_mitigate=0`: does NOT rescue a VM that is already
hung; testing whether it prevents recurrence.
- Pinned 7.0.2-7-pve via `proxmox-boot-tool kernel pin` and rebooted; so far
observing for stability.

This looks very similar to another report here:
G

Thread 'Proxmox VE compatibility issue with Intel I9-14900K?'

I just reinstalled Proxmox VE (9.2-1) on my Homeserver (Asus Rog Strix Z690-E Mainboard with Intel Core I9-14900K) because the server freezes while booting at different points. After fresh installation with "proxmox-kernel-7.0.2-6-pve-signed" reboot works. After updating to "proxmox-kernel-7.0.6-2-pve-signed", the server freezes again during boot process. Is there a compatibility issue with mainboard or cpu? I tried to find logs with specific errors, but nothing usefull. Memtest and cpu tests without errors, latest bios version installed. I now changed grub to boot "7.0.2-6". Thanks for help.

Questions
- Is this a known regression in the 7.0.6 base on Intel Raptor Lake (13th/14th
gen) hosts?
- Did split_lock_detect / bus-lock handling change between the 7.0.2 and 7.0.6
bases?
- Any recommended fix beyond pinning 7.0.2 / split_lock_mitigate=0, or is a fix
expected in a newer 7.0.x kernel?

Full `pveversion -v`, dmesg, and `qm config` available on request.

Thanks!
 
Regarding split lock detection, this is done on the kernel side. Please take a look at [1] for more information. Each time a split_lock is detected the CPU the kernel freezes the CPU for 10ms which can tank performance if it happens too often, unfortunately, the impact of a split lock cannot be determined by looking at the journal as it is only logged once, see [1] on how to check how often they are detected.


[1] https://pve.proxmox.com/wiki/Split_lock_detection
 
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