linux-kernel - Re: [Qemu-devel] [PATCH v7.5] kvm: notify host when the guest is panicked

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Message-ID: <500C5C91.3060505@gmail.com>
Date:	Sun, 22 Jul 2012 22:03:29 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	Wen Congyang <wency@...fujitsu.com>,
	Gleb Natapov <gleb@...hat.com>, kvm list <kvm@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	rusty@...tcorp.com.au
Subject: Re: [Qemu-devel] [PATCH v7.5] kvm: notify host when the guest is
 panicked

On 07/22/2012 09:14 PM, Anthony Liguori wrote:
> Sasha Levin <levinsasha928@...il.com> writes:
> 
>> On 07/21/2012 10:44 AM, 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
>>
>> Was the option of implementing a virtio-watchdog driver considered?
>>
>> You're basically re-implementing a watchdog, a guest-host interface and a set of protocols for guest-host communications.
>>
>> Why can't we re-use everything we have now, push a virtio watchdog
>> driver into drivers/watchdog/, and gain a more complete solution to
>> detecting hangs inside the guest.
> 
> The purpose of virtio is not to reinvent every possible type of device.
> There are plenty of hardware watchdogs that are very suitable to be used
> for this purpose.  QEMU implements quite a few already.
> 
> Watchdogs are not performance sensitive so there's no point in using
> virtio.

The issue here is not performance, but the adding of a brand new guest-host interface.

virtio-rng isn't performance sensitive either, yet it was implemented using virtio so there wouldn't be yet another interface to communicate between guest and host.

This patch goes ahead to add a "arch pv features" interface using ioports, without any idea what it might be used for beyond this watchdog.
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