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

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Date:	Wed, 21 Mar 2012 14:04:34 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...hat.com>
CC:	"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>,
	Gleb Natapov <gleb@...hat.com>,
	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 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.

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

>

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