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

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Date:	Wed, 14 Mar 2012 19:11:32 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Gleb Natapov <gleb@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH 0/2 v3] kvm: notify host when guest panicked

At 03/14/2012 06:48 PM, Avi Kivity Wrote:
> On 03/14/2012 12:46 PM, Gleb Natapov wrote:
>> On Wed, Mar 14, 2012 at 12:29:57PM +0200, Avi Kivity wrote:
>>> On 03/14/2012 12:26 PM, Wen Congyang wrote:
>>>>>> If so, is this channel visible to guest userspace? If the channle is visible to guest
>>>>>> userspace, the program running in userspace may write the same message to the channel.
>>>>>>
>>>>>
>>>>> Surely there's some kind of access control on channels.
>>>>
>>>> The virtio-serial depends on more things than touching the hypervisor. So I think touching
>>>> the hypervisor is more reliable than using virtio-serial device, and it is very simple and
>>>> easy to use.
>>>>
>>>> If we pass something from guest userspace to host, we can use virtio-serial. But If we pass
>>>> something from guest kernelspace to host, I still prefer to touch the hypervisor.
>>>
>>> There's no argument that it's easier.  My concern is different, we're
>>> adding more and more stuff to the hypervisor because it's easier, which
>>> bloats it.  Every time we do it we add to compatibility and security
>>> problems.
>>>
>>> The panic notification is *really* simple, so I don't expect it to cause
>>> a lot of problems.  But still, if it's possible not to change the
>>> hypervisor, we must make an effort in that direction.
>>>
>> One more point against using virtio-serial is that it will be likely
>> compiled as a module which means panic during early boot will not be
>> reported.
> 
> I don't think we want to use the driver.  Instead, have a small piece of
> code that resets the device and pushes out a string (the panic message?)
> without any interrupts etc.
> 
> It's still going to be less reliable than a hypercall, I agree.

Do you still want to use complicated and less reliable way?

I think the other ones prefer to touch the hypervisor.

Thanks
Wen Congyang

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