** 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) -- You received this bug notification because you are subscribed to linux in Ubuntu. Matching subscriptions: Bgg, Bmail, Nb 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 Status in linux package in Ubuntu: New Bug description: [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 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") To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2163620/+subscriptions
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