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

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Message-ID: <20120322073324.GZ22368@redhat.com>
Date:	Thu, 22 Mar 2012 09:33:24 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Avi Kivity <avi@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

On Wed, Mar 21, 2012 at 02:04:34PM -0500, Anthony Liguori wrote:
> On 03/13/2012 05:47 AM, Avi Kivity wrote:
> >On 03/13/2012 11:18 AM, Daniel P. Berrange wrote:
> >>On Mon, Mar 12, 2012 at 12:33:33PM +0200, Avi Kivity wrote:
> >>>On 03/12/2012 11:04 AM, Wen Congyang wrote:
> >>>>Do you have any other comments about this patch?
> >>>>
> >>>
> >>>Not really, but I'm not 100% convinced the patch is worthwhile.  It's
> >>>likely to only be used by Linux, which has kexec facilities, and you can
> >>>put talk to management via virtio-serial and describe the crash in more
> >>>details than a simple hypercall.
> >>
> >>As mentioned before, I don't think virtio-serial is a good fit for this.
> >>We want something that is simple&  guaranteed always available. Using
> >>virtio-serial requires significant setup work on both the host and guest.
> >
> >So what?  It needs to be done anyway for the guest agent.
> >
> >>Many management application won't know to make a vioserial device available
> >>to all guests they create.
> >
> >Then they won't know to deal with the panic event either.
> >
> >>Most administrators won't even configure kexec,
> >>let alone virtio serial on top of it.
> >
> >It should be done by the OS vendor, not the individual admin.
> >
> >>The hypercall requires zero host
> >>side config, and zero guest side config, which IMHO is what we need for
> >>this feature.
> >
> >If it was this one feature, yes.  But we keep getting more and more
> >features like that and we bloat the hypervisor.  There's a reason we
> >have a host-to-guest channel, we should use it.
> 
> The problem is that virtio-serial sucks for something like this.
> 
How do we know if we haven't tried :)

> We have two options I think:
> 
> 1) We could reserve a portion of the hypercall space to be deferred
> to userspace for stuff like this.
> 
> 2) We could invent a new hypercall like facility that was less
> bloated than virtio-serial for stuff like this using MMIO/PIO.
> 
> Regards,
> 
> Anthony Liguori
> 
> >

--
			Gleb.
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