Public bug reported:
== Problem Description ===
On a POWER11 system with the processor compatibility mode set to POWER10,
Ubuntu 26.10 guest installation fails to boot on a KVM-enabled host. When a
guest is created using virt-install and booted from the Ubuntu 26.10
installation ISO, the boot process hangs during early kernel initialization and
the installer does not proceed further.
HOST ENV:
OS : Ubuntu 26.10 (Stonking Stingray)
kernel : 7.0.0-14-generic
libvirt : libvirtd (libvirt) 12.0.0
qemu : QEMU emulator version 10.2.1
on host :
# lscpu
Architecture: ppc64le
Byte Order: Little Endian
CPU(s): 80
On-line CPU(s) list: 0-79
Model name: POWER10 (architected), altivec supported
Model: 2.0 (pvr 0082 0200)
Thread(s) per core: 8
Core(s) per socket: 10
Socket(s): 1
Virtualization features:
Hypervisor vendor: pHyp
Virtualization type: para
Caches (sum of all):
L1d: 640 KiB (20 instances)
L1i: 960 KiB (20 instances)
L2: 20 MiB (20 instances)
L3: 80 MiB (20 instances)
NUMA:
NUMA node(s): 3
NUMA node0 CPU(s):
NUMA node1 CPU(s): 0-79
NUMA node2 CPU(s):
Vulnerabilities:
Gather data sampling: Not affected
Ghostwrite: Not affected
Indirect target selection: Not affected
Itlb multihit: Not affected
L1tf: Not affected
Mds: Not affected
Meltdown: Not affected
Mmio stale data: Not affected
Old microcode: Not affected
Reg file data sampling: Not affected
Retbleed: Not affected
Spec rstack overflow: Not affected
Spec store bypass: Not affected
Spectre v1: Mitigation; __user pointer sanitization, ori31
speculation barrier enabled
Spectre v2: Mitigation; Software count cache flush (hardware
accelerated), Software link stack flush
Srbds: Not affected
Tsa: Not affected
Tsx async abort: Not affected
Vmscape: Not affected
Steps to re-create:
===================
- Setup KVM enabled host with Ubuntu26.10.
- Install libvirt and qemu packages required for bringing up GUests
- Create and boot an Ubuntu 26.10 KVM guest from the Ubuntu 26.10 installation
ISO on a POWER11 LPAR running in POWER10 compatibility mode using the following
command:
--logs--
/usr/bin/virt-install --connect=qemu:///system --hvm --accelerate --name 'vm'
--machine pseries --memory=10000 --vcpu=10,sockets=1,cores=10,threads=1
--import --nographics --os-variant ubuntu25.10 --serial pty --memballoon
model=virtio --controller type=scsi,model=virtio-scsi --disk
path=/home/ubuntu26_10.qcow2,bus=scsi,size=50,format=qcow2
--network=bridge=virbr0,model=virtio --boot emulator=/usr/bin/qemu-system-ppc64
--cdrom /home/ubuntu-26.10-snapshot2-live-server-ppc64el.iso
WARNING CDROM media does not print to the text console by default, so you
likely will not see text install output. You might want to use --location. See
the man page for examples of using --location with CDROM media
Starting install...
Allocating 'ubuntu26_10.qcow2'
| 50 GB 00:00:00
Creating domain...
| 00:00:00
Running text console command: virsh --connect qemu:///system console vm
Connected to domain 'vm'
Escape character is ^] (Ctrl + ])
Populating /vdevice methods
Populating /vdevice/vty@30000000
Populating /vdevice/nvram@71000000
Populating /pci@800000020000000
00 0800 (D) : 1af4 1000 virtio [ net ]
00 1000 (D) : 1af4 1004 virtio [ scsi ]
Populating /pci@800000020000000/scsi@2
SCSI: Looking for devices
100000000000000 DISK : "QEMU QEMU HARDDISK 2.5+"
100000100000000 CD-ROM : "QEMU QEMU CD-ROM 2.5+"
00 1800 (D) : 1b36 000d serial bus [ usb-xhci ]
00 2000 (D) : 1af4 1003 virtio [ serial ]
00 2800 (D) : 1af4 1002 legacy-device*
00 3000 (D) : 1af4 1005 legacy-device*
No NVRAM common partition, re-initializing...
Scanning USB
XHCI: Initializing
Using default console: /vdevice/vty@30000000
Welcome to Open Firmware
Copyright (c) 2004, 2017 IBM Corporation All rights reserved.
This program and the accompanying materials are made available
under the terms of the BSD License available at
http://www.opensource.org/licenses/bsd-license.php
Trying to load: from: /pci@800000020000000/scsi@2/disk@100000100000000 ...
Successfully loaded
Welcome to GRUB!
error: couldn't examine /ibm,secure-boot property.
error: unrecognized number.
GNU GRUB version 2.14
+----------------------------------------------------------------------------+
|*Try or Install Ubuntu Server |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
+----------------------------------------------------------------------------+
Use the ^ and v keys to select which entry is highlighted.
Press enter to boot the selected OS, `e' to edit the commands
before booting or `c' for a command-line.
OF stdout device is: /vdevice/vty@30000000
Preparing to boot Linux version 7.0.0-14-generic (buildd@bos03-ppc64el-029)
(powerpc64le-linux-gnu-gcc (Ubuntu 15.2.0-16ubuntu1) 15.2.0, GNU ld (GNU
Binutils for Ubuntu) 2.46) #14-Ubuntu SMP PREEMPT_DYNAMIC Mon Apr 13 11:10:37
UTC 2026 (Ubuntu 7.0.0-14.14-generic 7.0.0)
Detected machine type: 0000000000000101
command line: BOOT_IMAGE=/casper/vmlinux quiet ---
Max number of cores passed to firmware: 2048 (NR_CPUS = 2048)
Calling ibm,client-architecture-support...
== Comment: #2 ==
The patches are in ppc next now:
c1721e584244 KVM: PPC: Document KVM_PPC_GET_COMPAT_CAPS ioctl
8735048f54ec KVM: PPC: Book3S HV: Add support for compat CPU capabilities for
KVM on PowerNV
b76fb087efcd KVM: PPC: Book3S HV: Implement compat CPU capability retrieval for
KVM on PowerVM
ac3e65ddddf3 KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and wire up ioctl
884ea0283f4e KVM: PPC: Book3S HV: Validate arch_compat against host
compatibility mode
Please note that one of the dependent patches had already made it to
upstream.
e4de1b9cb3b5 ("powerpc/dt_cpu_ftrs: Set CPU_FTR_P11_PVR for Power11 and
later processors")
** Affects: kernel-package (Ubuntu)
Importance: Undecided
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
Status: New
** Tags: architecture-ppc64le bugnameltc-220722 severity-high
targetmilestone-inin2610
** Tags added: architecture-ppc64le bugnameltc-220722 severity-high
targetmilestone-inin2610
** Changed in: ubuntu
Assignee: (unassigned) => Ubuntu on IBM Power Systems Bug Triage
(ubuntu-power-triage)
** Package changed: ubuntu => kernel-package (Ubuntu)
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https://bugs.launchpad.net/bugs/2163620
Title:
[Ubuntu 26.10] : KVM guest boot hangs on POWER11 host when processor
compatibility mode is set to POWER10
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