linux-kernel - Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is panicked

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Message-ID: <87boidgvaq.fsf@codemonkey.ws>
Date:	Tue, 14 Aug 2012 13:53:01 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Marcelo Tosatti <mtosatti@...hat.com>,
	Yan Vugenfirer <yvugenfi@...hat.com>
Cc:	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

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.  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.

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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