Public bug reported: host Ubuntu 22.04 + Kernel 6.8 HWE OpenStack Epoxy (openstack-helm-based), AMD EPYC 9754 128-Core Processor
Qemu runs in a ubuntu-noble-based docker container. Package: qemu-system-x86 Version: 1:8.2.2+ds-0ubuntu1.9 Previous Qemu version was 1:6.2+dfsg-2ubuntu6.26 (runs in ubuntu-jammy- based container). After upgrading the cloud to OpenStack Epoxy and thus qemu 6.2 to qemu 8.2 as pointed above, we are seeing boot failures for new VMs using our largest flavor (~900GB RAM, 1GB hugepages, 112 vCPU). During early boot the guest reports virtio BAR reservation failures such as: virtio-pci ... BAR ... can't reserve virtio-pci: probe failed with error -16 When this occurs the virtio-scsi controller never initializes, so the root disk is not detected and the VM drops to initramfs with a missing root UUID. Smaller flavors appear unaffected. Comparing working vs failing instances shows the same device layout (virtio-scsi disk, virtio NIC, etc.), but the PCI MMIO window placement differs: Working host (older VM): 64-bit MMIO window at 0xe040000000 (above guest RAM end) Failing host (new VM): 64-bit MMIO window at 0xc040000000 (inside guest RAM range) When the MMIO window overlaps guest RAM, virtio BAR allocation fails with -EBUSY. Machine types Working VM: pc-i440fx-6.2 New VM: pc-i440fx-8.2 Both are still i440fx (BIOS) machines. The version change alone doesn’t appear to explain the issue but likely changes QEMU defaults (PCI hole sizing / BAR placement). Attaching XML for the failing VM as generated by OpenStack Nova (epoxy release) for libvirt 10.0 (from ubuntu 24.04) Rebuilding VM with q35-* machine type seems to solve the issue. We suspect this might be related to the following patch/fix "hw/i386/pc: Avoid overlap between CXL window and PCI 64" which is present in qemu 10.2.0 https://gitlab.com/qemu- project/qemu/-/commit/d1193481dee63442fc41e47ca6ebc4cd34f1f69c Please consider porting that patch to qemu 8.2 as in Ubuntu 24.04. ** Affects: qemu (Ubuntu) Importance: Undecided Status: Confirmed ** Attachment added: "libvirt 10.0 XML for large mem VM that fails on qemu 8.2" https://bugs.launchpad.net/bugs/2146021/+attachment/5955323/+files/large-vm-failing.xml -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2146021 Title: Qemu 8.2 fails to boot VM with very large memory To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/2146021/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
