** Description changed:
+ [Impact]
+
+ 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.
+
+ [Fix]
+
+ Apply the following patches from linux-next:
+ - 884ea0283f4e KVM: PPC: Book3S HV: Validate arch_compat against host
compatibility mode
+ - ac3e65ddddf3 KVM: PPC: Introduce KVM_CAP_PPC_COMPAT_CAPS and wire up ioctl
+ - b76fb087efcd KVM: PPC: Book3S HV: Implement compat CPU capability retrieval
+ for KVM on PowerVM
+ - 8735048f54ec KVM: PPC: Book3S HV: Add support for compat CPU capabilities
for KVM on PowerNV
+ - c1721e584244 KVM: PPC: Document KVM_PPC_GET_COMPAT_CAPS ioctl
+
+ [Test Plan]
+
+ - 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:
+ ```
+ /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
+ ```
+
+ [Regression Potential]
+
+ The change is confined to powerpc nested virtualization code.
+ Users of nested virtualization in powerpc may be affected.
+
+ ---
+
== 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
+ Byte Order: Little Endian
CPU(s): 80
- On-line CPU(s) list: 0-79
+ 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
+ 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
+ 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)
+ 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):
+ 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
+ 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 ]
+ 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*
+ 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
+ XHCI: Initializing
Using default console: /vdevice/vty@30000000
- Welcome to Open Firmware
+ 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
-
+ 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
+ GNU GRUB version 2.14
-
+----------------------------------------------------------------------------+
- |*Try or Install Ubuntu Server
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
- |
|
-
+----------------------------------------------------------------------------+
+
+----------------------------------------------------------------------------+
+ |*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.
+ 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")
** Also affects: linux (Ubuntu)
Importance: Undecided
Status: New
** No longer affects: kernel-package (Ubuntu)
--
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Bugs, which is subscribed to Ubuntu.
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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