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+pvpanic device is a simulated ISA device, through which guest panic
+event is sent to qemu, and a QMP event is generated. This allows
+management apps(e.g. libvirt) to be notified and respond to the
+pvpanic uses port 0x505 by default to receive panic event from guest.
+The port is configurable by specifying ioport property.
+pvpanic device is defined with ACPI ID "QEMU0001". To send panic
+event, guest evaluates method WRPT, specifying a byte, bit 0 set,
+as argument. Other bits are reserved.
+To use it, one will have to:
+1. add the device by specifying `-device pvpanic' in the qemu command
+2. load pvpanic device driver in guest OS.
+The management app has the options of waiting for GUEST_PANICKED events,
+and/or polling for guest-panicked RunState, to learn when the pvpanic
+device has fired a panic event.