Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

[Wen Congyang]

At 03/21/2012 05:11 PM, Gleb Natapov Wrote:
> On Wed, Mar 21, 2012 at 08:56:03AM +0800, Wen Congyang wrote:
>> At 03/20/2012 11:45 PM, Gleb Natapov Wrote:
>>> On Tue, Mar 20, 2012 at 05:59:16PM +0800, Wen Congyang wrote:
>>>> At 03/19/2012 03:33 PM, Wen Congyang Wrote:
>>>>> At 03/08/2012 03:57 PM, Wen Congyang Wrote:
>>>>>> We can know the guest is paniced 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 crashed. If management
>>>>>> app does not do auto dump, the guest's user can do dump by hand if
>>>>>> he sees the guest is paniced.
>>>>>>
>>>>>> I touch the hypervisor instead of using virtio-serial, because
>>>>>> 1. it is simple
>>>>>> 2. the virtio-serial is an optional device, and the guest may
>>>>>>    not have such device.
>>>>>>
>>>>>> Changes from v2 to v3:
>>>>>> 1. correct spelling
>>>>>>
>>>>>> Changes from v1 to v2:
>>>>>> 1. split up host and guest-side changes
>>>>>> 2. introduce new request flag to avoid changing return values.
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>>>>>>
>>>>>
>>>>>
>>>>> Hi all:
>>>>>
>>>>> we neet this feature, but we don't decide how to implement it.
>>>>> We have two solution:
>>>>> 1. use vmcall
>>>>> 2. use virtio-serial.
>>>>>
>>>>> I will not change this patch set before we decide how to do it.
>>>>> Can we make a decision recent days?
>>>>
>>>> Anybody can decide which solution to use?
>>>>
>>> To make an informed decision we need to have at least raw idea how
>>> virtio-serial variant will look.
>>
>> Hmm, I think we can do this:
>> 1. reset the virtio-serial device or reset the port we use to notice
>>    the host that guest is panicked.
>> 2. write some specific messages to the port
>>
>> So the port should have fixed name. If this port is opened by the userspace
>> before the guest is paniced, I am not sure whether we can use it(because a
>> port only can be opened once at the same time).
> Yes, IMO we should dedicate one virtio-serial port for panic
> notifications. Just like we dedicate one for a console.
> 
>> We cannot call any function in the module, so we may need to write a simple
>> driver for virtio-serial(like diskdump's disk driver).
>>
> netconsole uses standard NIC drivers in polling mode to send OOPSes
> over the network and it mostly works. So I think using virtio-serial
> driver is not out of question, but with IRQ disabled of course.

The code for netconsole is in which file?
Another question: we cannot call the function in the module directly in the
kernel.

> 
>> I donot know how to implement it now. But I guess that it may be complicated.
>>
> Look at drivers/char/ipmi/ipmi_msghandler.c. It has code to send panic
> event over IMPI. The code is pretty complex. Of course if we a going to
> implement something more complex than simple hypercall for panic
> notification we better do something more interesting with it than just
> saying "panic happened", like sending stack traces on all cpus for
> instance.

If we implement it by virtio-serial, I agree with passing more useful message
to host.

Thanks
Wen Congyang

> 
> --
>                       Gleb.
>