Re: [Qemu-devel] [PATCH] vl: allow "cont" from panicked state

[Laszlo Ersek <lersek@redhat.com>]

On 08/21/13 17:32, Paolo Bonzini wrote:

> To support 1.5, libvirt should simply be ready to react to unanticipated
> GUEST_PANICKED events.  reboot-on-panic will simply be broken for 1.5
> and Linux 3.10+ guests. :(

I'm probably misunderstanding the discussion, but it might be possible
to disable pvpanic even in 1.5 from the host side, with the following hack:

  -global pvpanic.ioport=0

In qemu, this will either configure a working pvpanic device on ioport
0, or the pvpanic device will be genuinely broken. At least it doesn't
(obviously) break other stuff (in v1.5.2):

(qemu) info mtree
I/O
0000000000000000-000000000000ffff (prio 0, RW): io
  0000000000000000-0000000000000000 (prio 0, RW): pvpanic
  0000000000000000-0000000000000007 (prio 0, RW): dma-chan

(qemu) info qtree
bus: main-system-bus
  dev: i440FX-pcihost, id ""
    bus: pci.0
      dev: PIIX3, id ""
        bus: isa.0
          dev: pvpanic, id ""
            ioport = 0

Either way, the "etc/pvpanic-port" fw_cfg file will contain 0, and
SeaBIOS will interpret it as "no pvpanic device". It will report the
same to the Linux guest too (_STA will return 0 for QEMU0001;
pvpanic_add() --> -ENODEV). Thus, no pvpanic notifier should be
registered, and reboot-on-panic should be reachable in the guest.

A horrible hack, certainly.

Laszlo