linux-kernel - Re: [PATCH] kvm: notify host when guest paniced

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Date:	Wed, 29 Feb 2012 18:17:27 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Gleb Natapov <gleb@...hat.com>, kvm list <kvm@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	linux-kernel@...r.kernel.org, qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [PATCH] kvm: notify host when guest paniced

At 02/29/2012 06:08 PM, Avi Kivity Wrote:
> On 02/29/2012 12:05 PM, Gleb Natapov wrote:
>> On Wed, Feb 29, 2012 at 12:00:41PM +0200, Avi Kivity wrote:
>>> On 02/29/2012 11:55 AM, Gleb Natapov wrote:
>>>>>>
>>>>>
>>>>> How about using a virtio-serial channel for this?  You can transfer any
>>>>> amount of information (including the dump itself).
>>>>>
>>>> Isn't it unreliable after the guest panicked? 
>>>
>>> So is calling hypercalls, or dumping, or writing to the screen.  Of
>>> course calling a hypercall is simpler and so is more reliable.
>>>
>> Yes, crash can be so severe that it is not even detected by a kernel
>> itself, so not OOPS message even printed. But in most cases if kernel is
>> functional enough to print OOPS it is functional enough to call single
>> hypercall instruction.
> 
> Why not print the oops to virtio-serial?  Or even just a regular serial
> port?  That's what bare metal does.

If virtio-serial's driver has bug or the guest doesn't have such device...

> 
>>>> Having special kdump
>>>> kernel that transfers dump to a host via virtio-serial channel though
>>>> sounds interesting. May be that's what you mean.
>>>
>>> Yes.  The "panic, starting dump" signal should be initiated by the
>>> panicking kernel though, in case the dump fails.
>>>
>> Then panic hypercall sounds like a reasonable solution.
> 
> It is, but I'm trying to see if we can get away with doing nothing.
> 

If we have a reliable way with doing nothing, it is better. But I donot
find such way.

Thanks
Wen Congyang

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