linux-kernel - Re: [PATCH v11] kvm: notify host when the guest is panicked

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Date:	Wed, 31 Oct 2012 09:48:04 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Hu Tao <hutao@...fujitsu.com>, kvm list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Gleb Natapov <gleb@...hat.com>,
	Blue Swirl <blauwirbel@...il.com>,
	Eric Blake <eblake@...hat.com>,
	Andrew Jones <drjones@...hat.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Luiz Capitulino <lcapitulino@...hat.com>
Subject: Re: [PATCH v11] kvm: notify host when the guest is panicked

At 10/31/2012 09:12 AM, Marcelo Tosatti Wrote:
> On Thu, Oct 25, 2012 at 11:42:32AM +0800, Hu Tao 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
> 
> It has been asked earlier why a simple virtio device is not usable
> for this (with no response IIRC).

1. We can't use virtio device when the kernel is booting.
2. The virtio's driver can be built as a module, and if it is not loaded
   and the kernel is panicked, there is no way to notify the host.
3. I/O port is more reliable than virtio device.
   If virtio's driver has some bug, and it cause kernel panicked, we can't
   use it. The I/O port is more reliable because it only depends on notifier
   chain(If we use virtio device, it also depends on notifier chain).

Thanks
Wen Congyang

> 
> Also, there is no high level documentation: purpose of the interface,
> how a management application should use it, etc.
> 
> 

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