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

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Date:	Wed, 21 Mar 2012 17:04:14 +0000
From:	"Daniel P. Berrange" <berrange@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	minyard@....org, Corey Minyard <tcminyard@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	Wen Congyang <wency@...fujitsu.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>
Subject: Re: [PATCH 0/2 v3] kvm: notify host when guest panicked

On Wed, Mar 21, 2012 at 06:25:16PM +0200, Avi Kivity wrote:
> On 03/21/2012 06:18 PM, Corey Minyard wrote:
> >
> >> Look at drivers/char/ipmi/ipmi_msghandler.c. It has code to send panic
> >> event over IMPI. The code is pretty complex. Of course if we a going to
> >> implement something more complex than simple hypercall for panic
> >> notification we better do something more interesting with it than just
> >> saying "panic happened", like sending stack traces on all cpus for
> >> instance.
> >
> > I doubt that's the best example, unfortunately.  The IPMI event log
> > has limited space and it has to be send a little piece at a time since
> > each log entry is 14 bytes.  It just prints the panic string, nothing
> > else.  Not that it isn't useful, it has saved my butt before.
> >
> > You have lots of interesting options with paravirtualization.  You
> > could, for instance, create a console driver that delivered all
> > console output efficiently through a hypercall.  That would be really
> > easy.  Or, as you mention, a custom way to deliver panic information. 
> > Collecting information like stack traces would be harder to
> > accomplish, as I don't think there is currently a way to get it except
> > by sending it to printk.
> 
> That already exists; virtio-console (or serial console emulation) can do
> the job.
> 
> In fact the feature can be implemented 100% host side by searching for a
> panic string signature in the console logs.

You can even go one better and search for the panic string in the
guest memory directly, which is what virt-dmesg does :-)

  http://people.redhat.com/~rjones/virt-dmesg/

Daniel
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