Message-Id: <87144629-6510-485F-B6B4-D53A171B7797@redhat.com>
Date:	Wed, 15 Aug 2012 14:38:47 +0300
From:	Yan Vugenfirer <yvugenfi@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	qemu-devel <qemu-devel@...gnu.org>, Avi Kivity <avi@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked


On Aug 14, 2012, at 10:35 PM, Anthony Liguori wrote:

> Marcelo Tosatti <mtosatti@...hat.com> writes:
> 
>> On Tue, Aug 14, 2012 at 01:53:01PM -0500, Anthony Liguori wrote:
>>> Marcelo Tosatti <mtosatti@...hat.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
> 
> Not sure the semantics of blink but that might be a good place for a
> pvops hook.
> 
>> 
>> 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.
> 
> I must admit, I don't know why a new runstate is necessary/useful.  The
> kernel shouldn't have to care about the difference between a halted guest
> and a panicked guest.  That level of information belongs in userspace IMHO.
> 
>> Can this new infrastructure be used by other architectures?
> 
> I guess I don't understand why the kernel side of this isn't anything
> more than a paravirt op hook that does a single outb() with the
> remaining logic handled 100% in QEMU.
> 
>> Do you consider allowing support for Windows as overengineering?
> 
> I don't think there is a way to hook BSOD on Windows so attempting to
> engineer something that works with Windows seems odd, no?
> 

Actually there is a way (http://msdn.microsoft.com/en-us/library/windows/hardware/ff553105(v=vs.85).aspx). That's what I just mentioned already done in Windows virtio-net driver. 


Best regards,
Yan.

> Regards,
> 
> Anthony Liguori
> 
>> 
>>> 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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