linux-kernel - Re: [PATCH] kvm: notify host when guest paniced

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Date:	Wed, 29 Feb 2012 18:31:24 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	"Daniel P. Berrange" <berrange@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [PATCH] kvm: notify host when guest paniced

At 02/29/2012 06:05 PM, Avi Kivity Wrote:
> On 02/29/2012 11:58 AM, Daniel P. Berrange wrote:
>>>
>>> How about using a virtio-serial channel for this?  You can transfer any
>>> amount of information (including the dump itself).
>>
>> When the guest OS has crashed, any dumps will be done from the host
>> OS using libvirt's core dump mechanism. The guest OS isn't involved
>> and is likely too dead to be of any use anyway. Likewise it is
>> quite probably too dead to work a virtio-serial channel or any
>> similarly complex device. We're really just after the simplest
>> possible notification that the guest kernel has paniced.
> 
> If it's alive enough to panic, it's alive enough to kexec its kdump
> kernel.  After that it can do anything.
> 
> Guest-internal dumps are more useful IMO that host-initiated dumps.  In

Yes, guest-internal dump is better than host dump. But the user may not
start guest-internal dump or guest-internal dump failed. So we need the
following feature:
1. If the guest-internal dump does not work, the guest's status is 'crashed'.
   And then the user does the host dump.
2. If the guest-internal dump is working, the guest's status should be
   'dumping'. The user see this status and know the guest has paniced, and
    the guest-internal dump is working.

Thanks
Wen Congyang

> a cloud, the host-initiated dump is left on the host, outside the reach
> of the guest admin, outside the guest image where all the symbols are,
> and sometimes not even on the same host if a live migration occurred. 
> It's more useful in small setups, or if the problem is in the
> hypervisor, not the guest.
> 

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