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

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Date:	Wed, 21 Mar 2012 18:24:38 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	minyard@....org
Cc:	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>,
	Avi Kivity <avi@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	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 11:18:16AM -0500, 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.
> 
I gave ipmi example just to show that others do complex things on panic,
not as an example of what we should do on a guest panic.

> 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.
> 
Why using hypercall for that though? You can do that with
virtio-console. Make it zero config: virtio-console detected -> send
console output there.

--
			Gleb.
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