[Bug 1859310] Re: libvirt probing fails due to assertion failure with KVM and 'none' machine type

[Thomas Huth]

** Changed in: qemu
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1859310

Title:
  libvirt probing fails due to assertion failure with KVM and 'none'
  machine type

Status in QEMU:
  Fix Released

Bug description:
  Using libvirt on Ubuntu 19.10, I get the following error when I try to
  set <emulator> to the latest qemu from git (commit dc65a5bdc9):

      error: internal error: Failed to start QEMU binary /usr/local/bin
  /qemu-system-x86_64 for probing:
  /home/joey/git/qemu/target/i386/kvm.c:2176:kvm_arch_init: Object
  0x564bfd5c3200 is not an instance of type x86-machine

  Qemu command line to reproduce:

      sudo x86_64-softmmu/qemu-system-x86_64 -machine 'none,accel=kvm'

  Commit ed9e923c3c (Dec 12, 2019) introduced the issue by removing an
  object_dynamic_cast call.  In this scenario, kvm_arch_init is passed
  an instance of "none-machine" instead of "x86-machine".

  The following one-line change to target/i386/kvm.c reintroduces the
  cast:

       if (kvm_check_extension(s, KVM_CAP_X86_SMM) &&
  +        object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE) &&
           x86_machine_is_smm_enabled(X86_MACHINE(ms))) {
           smram_machine_done.notify = register_smram_listener;
           qemu_add_machine_init_done_notifier(&smram_machine_done);
       }

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