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

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Message-ID: <4F607789.4010109@redhat.com>
Date:	Wed, 14 Mar 2012 12:48:41 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Wen Congyang <wency@...fujitsu.com>,
	"Daniel P. Berrange" <berrange@...hat.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>,
	Amit Shah <amit.shah@...hat.com>
Subject: Re: [PATCH 0/2 v3] kvm: notify host when guest panicked

On 03/14/2012 12:46 PM, Gleb Natapov wrote:
> On Wed, Mar 14, 2012 at 12:29:57PM +0200, Avi Kivity wrote:
> > On 03/14/2012 12:26 PM, Wen Congyang wrote:
> > > >> If so, is this channel visible to guest userspace? If the channle is visible to guest
> > > >> userspace, the program running in userspace may write the same message to the channel.
> > > >>
> > > > 
> > > > Surely there's some kind of access control on channels.
> > >
> > > The virtio-serial depends on more things than touching the hypervisor. So I think touching
> > > the hypervisor is more reliable than using virtio-serial device, and it is very simple and
> > > easy to use.
> > >
> > > If we pass something from guest userspace to host, we can use virtio-serial. But If we pass
> > > something from guest kernelspace to host, I still prefer to touch the hypervisor.
> > 
> > There's no argument that it's easier.  My concern is different, we're
> > adding more and more stuff to the hypervisor because it's easier, which
> > bloats it.  Every time we do it we add to compatibility and security
> > problems.
> > 
> > The panic notification is *really* simple, so I don't expect it to cause
> > a lot of problems.  But still, if it's possible not to change the
> > hypervisor, we must make an effort in that direction.
> > 
> One more point against using virtio-serial is that it will be likely
> compiled as a module which means panic during early boot will not be
> reported.

I don't think we want to use the driver.  Instead, have a small piece of
code that resets the device and pushes out a string (the panic message?)
without any interrupts etc.

It's still going to be less reliable than a hypercall, I agree.

-- 
error compiling committee.c: too many arguments to function

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