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SubjectRe: [PATCH] kvm/x86/vmx: report KVM_SYSTEM_EVENT_CRASH on triple fault
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On 28/03/2017 13:46, Josh Poimboeuf wrote:
> On Tue, Mar 28, 2017 at 03:51:01AM -0400, Paolo Bonzini wrote:
>>
>>> While debugging a kernel issue, I found that QEMU always reboots when an
>>> x86 triple fault occurs, which complicates debugging. QEMU and libvirt
>>> have a facility for creating a dump when KVM reports
>>> KVM_SYSTEM_EVENT_CRASH. So change the VMX triple fault handler to do
>>> that. This gives user space the ability to decide whether to dump,
>>> pause, shutdown, or reboot.
>>
>> You probably want QEMU's -no-reboot option.
>>
>> Triple faults are already reported to userspace with KVM_EXIT_SHUTDOWN,
>> and it's up to userspace to decide what to do with it. This patch cannot
>> be applied, because there are guests that do a triple-fault intentionally
>> in order to reset the machine.
>
> Ok. Any idea how to force libvirt to create a dump? It has a
> 'coredump-destroy' option, but that only seems to work with 'on_crash':
>
> https://libvirt.org/formatdomain.html#elementsEvents

Probably QEMU, when invoked with -no-shutdown -no-reboot, should treat
KVM_EXIT_SHUTDOWN as a panic. I can have a go at it, but note that QEMU
is now in hard freeze for the next release, so it will take a while.

However you're using libvirt and it doesn't use -no-reboot.

It's probably possible for libvirt to use -no-reboot more often. The
price would be that if libvirtd crashes and a VM wants to reset, then
the VM gets stuck.

Alternatively, we could generalize -no-shutdown and -no-reboot to
something like:

-action reset=stop|restart|quit,
poweroff=stop|quit,
triple-fault=stop|panic|restart|quit

and teach libvirt about it. The current semantics map relatively easily
to the new option:

| reset | poweroff | triple-fault
--------------------------+-------------+------------+-------------------
no option | restart | quit | restart
-no-shutdown | restart | stop | restart
-no-reboot | quit | quit | quit
-no-shutdown -no-reboot | stop | stop | stop (panic?)

Paolo

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