Re: Can't load bzImage crashkernel on xen system with 32 bit kernel

From: David Vrabel <david.vrabel@citrix.com>
To: Anthony Wright <anthony@overnetdata.com>,
	WANG Chao <chaowang@redhat.com>
Cc: Daniel Kiper <daniel.kiper@oracle.com>,
	Simon Horman <horms@verge.net.au>,
	kexec@lists.infradead.org
Subject: Re: Can't load bzImage crashkernel on xen system with 32 bit kernel
Date: Fri, 11 Jul 2014 13:17:21 +0100	[thread overview]
Message-ID: <53BFD5D1.2080207@citrix.com> (raw)
In-Reply-To: <53BFCA2C.6010403@overnetdata.com>

On 11/07/14 12:27, Anthony Wright wrote:
> On 11/07/2014 10:38, David Vrabel wrote:
>> On 11/07/14 08:58, WANG Chao wrote:
>>> On 07/10/14 at 11:11am, Anthony Wright wrote:
>>>> Hi Chao,
>>>>
>>>> Thanks for looking at this.
>>>>
>>>> On 10/07/2014 08:47, WANG Chao wrote:
>>>>> Hi, Anthony
>>>>>
>>>>> On 07/08/14 at 11:34am, Anthony Wright wrote:
>>>>>> After successfully modifying kexec-tools to get it to load a crashkernel
>>>>>> on a standard 32 bit linux 3.10.17 kernel, I tried to get it to load the
>>>>>> same crashkernel on the same 32 bit linux kernel running under xen
>>>>>> 4.4.0, but get the error "Cannot load <kernel-path>".
>> Are you trying to do an in-guest kexec or are you trying to kexec from Xen?
>>
>> If it's the latter, it should just work with 32 and 64-bit images, Xen
>> 4.4 and kexec-tools 2.0.5 or later.
>>
>> In-guest kexec doesn't work at all.
>>
>> David
> I'm trying to do the kexec from within a 32 bit linux 3.10.17 Dom0
> running under a 64 bit xen 4.4.0. When you say 'guest', does that mean
> DomU's or does that include Dom0 as well? If it includes Dom0 could you
> point me at some documentation to explain how/if it's possible to set up
> kexec/kdump for Dom0.
> 
> I have a Dom0 kernel that's crashing infrequently. I can't reproduce it
> easily and all the standard diagnostic techniques haven't been very
> helpful. I'd hoped to generate a crashdump using kexec/kdump to help
> diagnose the problem.

I would suggest trying a Xen kexec and exec'ing your crashdump kernel
(which will then be running on baremetal).

You will need to reserve a region of memory for the crash kernel on the
Xen command line (e.g., crashkernel=64M@32M) and use kexec-tools 2.0.5
or later.

We don't actually collect memory dumps from this environment (only basic
PCPU/VCPU state, Xen/dom0 backtraces, and console logs) so I'm not sure
what the status of tools for this are.  Daniel Kiper might know.

David

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