Public bug reported:
It's a KVM-based QEMU/libvirt virtual machine of Windows 11 quite
carefully tuned back in the day I installed it to match my processor
more closely and allow me to use nested virtualization. It worked fine
until this morning when I upgraded the kernel to version
7.3.0-5-generic. Since then the split lock mitigation has caused my VM
to crash at boot 100% of the times.
$ uname -a
Linux cn 7.3.0-5-generic #5-Ubuntu SMP PREEMPT_DYNAMIC Mon Sep 14 11:40:59 UTC
2026 x86_64 GNU/Linux
# Before the crash:
$ sudo dmesg | grep -iE 'kvm|vmx|svm|handle_exception'
[ 0.157404] x86/fpu: Supporting XSAVE feature 0x1000: 'Control-flow Kernel
registers (KVM only)'
# Right after the crash
$ sudo dmesg | grep -iE 'kvm|vmx|svm|handle_exception'
[ 0.157404] x86/fpu: Supporting XSAVE feature 0x1000: 'Control-flow Kernel
registers (KVM only)'
[ 96.777554] x86/split lock detection: #AC: CPU 7/KVM/15877 took a split_lock
trap at address: 0xfffff8047f4e5cdd
The interesting dmesg line is:
[ 96.777554] x86/split lock detection: #AC: CPU 7/KVM/15877 took a split_lock
trap at address: 0xfffff8047f4e5cdd
The same device and VM booted with kernel 7.0.0-30-generic works fine. I
imagine we must have just changed the policy around what to do when a
split lock event happens. With 7.3 I have:
$ cat /proc/sys/kernel/split_lock_mitigate
1
Just disabling it didn't solve the problem.
I honestly don't know if this is really a kernel problem per se, because if all
that changed was the split lock mitigation but not the detection, then it means
the problem existed before but was just tolerated.
My CPU:
Model name: Intel(R) Core(TM) i9-14900HX
CPU family: 6
Model: 183
Thread(s) per core: 2
Core(s) per socket: 24
Socket(s): 1
Virtualization features:
Virtualization: VT-x
Caches (sum of all):
L1d: 896 KiB (24 instances)
L1i: 1.3 MiB (24 instances)
L2: 32 MiB (12 instances)
L3: 36 MiB (1 instance)
NUMA:
NUMA node(s): 1
NUMA node0 CPU(s): 0-31
ProblemType: Bug
DistroRelease: Ubuntu 26.10
Package: linux-image-7.3.0-5-generic 7.3.0-5.5
ProcVersionSignature: Ubuntu 7.3.0-5.5-generic 7.3.0-rc3
Uname: Linux 7.3.0-5-generic x86_64
NonfreeKernelModules: zfs
ApportVersion: 2.36.0-0ubuntu1
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: [email protected] 10129 F....
wireplumber
/dev/snd/seq: [email protected] 10113 F....
pipewire
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Fri Sep 18 14:35:41 2026
InstallationDate: Installed on 2025-04-06 (530 days ago)
InstallationMedia: Ubuntu 24.04.2 LTS "Noble Numbat" - Release amd64 (20250215)
MachineType: System76 Adder WS
ProcEnviron:
LANG=pt_BR.UTF-8
PATH=(custom, no user)
SHELL=/usr/bin/bash
TERM=xterm-256color
XDG_RUNTIME_DIR=<set>
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-7.3.0-5-generic
root=/dev/mapper/ubuntu--vg-ubuntu--lv ro quiet splash pcie_aspm=on
crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M
SourcePackage: linux
UpgradeStatus: Upgraded to stonking on 2026-08-19 (30 days ago)
dmi.bios.date: 06/28/2024
dmi.bios.release: 0.0
dmi.bios.vendor: coreboot
dmi.bios.version: 2024-07-08_926f73d
dmi.board.name: Adder WS
dmi.board.vendor: System76
dmi.board.version: addw4
dmi.chassis.type: 9
dmi.chassis.vendor: System76
dmi.ec.firmware.release: 0.0
dmi.modalias:
dmi:bvncoreboot:bvr2024-07-08_926f73d:bd06/28/2024:br0.0:efr0.0:svnSystem76:pnAdderWS:pvraddw4:rvnSystem76:rnAdderWS:rvraddw4:cvnSystem76:ct9:cvr:sku:pfa:
dmi.product.name: Adder WS
dmi.product.version: addw4
dmi.sys.vendor: System76
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug stonking wayland-session
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/2167740
Title:
split lock detection crashed KVM virtual machine boot
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2167740/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
