Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Aug 14, 2012 at 01:53:01PM -0500, Anthony Liguori wrote:
> Marcelo Tosatti <mtosatti@redhat.com> writes:
> 
> > On Tue, Aug 14, 2012 at 05:55:54PM +0300, Yan Vugenfirer wrote:
> >> 
> >> On Aug 14, 2012, at 1:42 PM, Jan Kiszka wrote:
> >> 
> >> > On 2012-08-14 10:56, Daniel P. Berrange wrote:
> >> >> On Mon, Aug 13, 2012 at 03:21:32PM -0300, Marcelo Tosatti wrote:
> >> >>> On Wed, Aug 08, 2012 at 10:43:01AM +0800, Wen Congyang wrote:
> >> >>>> We can know the guest is panicked when the guest runs on xen.
> >> >>>> But we do not have such feature on kvm.
> >> >>>> 
> >> >>>> Another purpose of this feature is: management app(for example:
> >> >>>> libvirt) can do auto dump when the guest is panicked. If management
> >> >>>> app does not do auto dump, the guest's user can do dump by hand if
> >> >>>> he sees the guest is panicked.
> >> >>>> 
> >> >>>> We have three solutions to implement this feature:
> >> >>>> 1. use vmcall
> >> >>>> 2. use I/O port
> >> >>>> 3. use virtio-serial.
> >> >>>> 
> >> >>>> We have decided to avoid touching hypervisor. The reason why I choose
> >> >>>> choose the I/O port is:
> >> >>>> 1. it is easier to implememt
> >> >>>> 2. it does not depend any virtual device
> >> >>>> 3. it can work when starting the kernel
> >> >>> 
> >> >>> How about searching for the "Kernel panic - not syncing" string 
> >> >>> in the guests serial output? Say libvirtd could take an action upon
> >> >>> that?
> >> >> 
> >> >> No, this is not satisfactory. It depends on the guest OS being
> >> >> configured to use the serial port for console output which we
> >> >> cannot mandate, since it may well be required for other purposes.
> >> > 
> >> Please don't forget Windows guests, there is no console and no "Kernel Panic" string ;)
> >> 
> >> What I used for debugging purposes on Windows guest is to register a bugcheck callback in virtio-net driver and write 1 to VIRTIO_PCI_ISR register.
> >> 
> >> Yan. 
> >
> > Considering whether a "panic-device" should cover other OSes is also \

> > something to consider. Even for Linux, is "panic" the only case which
> > should be reported via the mechanism? What about oopses without panic? 
> >
> > Is the mechanism general enough for supporting new events, etc.
> 
> Hi,
> 
> I think this discussion is gone of the deep end.
> 
> Forget about !x86 platforms.  They have their own way to do this sort of
> thing.  

The panic function in kernel/panic.c has the following options, which
appear to be arch independent, on panic:

- reboot 
- blink

None are paravirtual interfaces however.

> Think of this feature like a status LED on a motherboard.  These
> are very common and usually controlled by IO ports.
> 
> We're simply reserving a "status LED" for the guest to indicate that it
> has paniced.  Let's not over engineer this.

My concern is that you end up with state that is dependant on x86.

Subject: [PATCH v8 3/6] add a new runstate: RUN_STATE_GUEST_PANICKED

Having the ability to stop/restart the guest (and even introducing a 
new VM runstate) is more than a status LED analogy.

Can this new infrastructure be used by other architectures?

Do you consider allowing support for Windows as overengineering?

> Regards,
> 
> Anthony Liguori
> 
> >
> >> 
> >> > Well, we have more than a single serial port, even when leaving
> >> > virtio-serial aside...
> >> > 
> >> > Jan
> >> > 
> >> > -- 
> >> > Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
> >> > Corporate Competence Center Embedded Linux
> >> > --
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