Notes about pvpanic
Overview
pvpanic, which is a paravirtualized device emulated by QEMU and used by the guest OS to report to the VMM when it experiences a panic/crash. This mechanism allows a guest OS kernel to signal the hypervisor when it panics, before any crash dump is collected.
pvpanic device
pvpanic device is a simulated device, through which a 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 event.
The management app has the option of waiting for GUEST_PANICKED events, and/or polling for guest-panicked RunState, to learn when the pvpanic device has fired a panic event.
The pvpanic device can be implemented as an ISA device (using IOPORT) or as a PCI device.
crash_kexec_post_notifiers
During initialization, the pvpanic module registers a callback with the panic_notifier_list notifier chain. When the kernel panics, the value of crash_kexec_post_notifiers determines whether or not the callbacks registered in the panic_notifier_list are invoked before kexec’ing into the capture kernel which will collect the crash dump. The panic() code in kernel/panic.c is extensively commented and worth a look if you are interested in the details.
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