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

[David Vrabel]

On 14/07/14 12:01, Anthony Wright wrote:
> On 11/07/2014 13:17, David Vrabel wrote:
>> 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 at 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
> I had the 'crashkernel=128M' parameter on the Dom0 linux kernel cmdline.
> Removing it from the Dom0 linux kernel command line and placing it on
> the Xen command line changed things, but unfortunately it still doesn't
> work.

Try explicitly placing the crash region at a known address as I
suggested above.

> I get the error message 'failed to get crash region from hypervisor'. On
> further investigation the call to xc_kexec_get_range() fails returning
> -1 with an errno of 34 (Numerical result out of range). According to the
> xen kexec documentation that I could find
> (http://xenbits.xen.org/docs/4.4-testing/misc/kexec_and_kdump.txt),
> there should be a 'Crash kernel' entry in /proc/iomem, however when I
> look, no such entry exists. I do wonder if this is an error in the
> documentation as I would expect a crashkernel= entry on the linux kernel
> command line to create such an entry in /proc/iomem, but was suprised
> when the documentation says the entry is created when you put
> crashkernel= on the xen command line.

3.x kernels do not add entries into /proc/iomem.

David