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Re: [Xen-devel] [Xen-users] crashkernel doesn't work with linux-2.6.32-dom0

On Thu, Feb 16, 2012 at 6:23 AM, Daniel Kiper <dkiper@xxxxxxxxxxxx> wrote:
> On Thu, Feb 16, 2012 at 09:01:20AM +0000, Jan Beulich wrote:
>> >>> On 16.02.12 at 08:29, Philipp Hahn <hahn@xxxxxxxxxxxxx> wrote:
>> > Hello,
>> >
>> > Am Donnerstag 16 Februar 2012 02:22:30 schrieben Sie:
>> >> On Tue, Feb 14, 2012 at 10:07 AM, Eric Camachat <eric.camachat@xxxxxxxxx>
>> > wrote:
>> >> > On Tue, Feb 14, 2012 at 12:07 AM, Philipp Hahn <hahn@xxxxxxxxxxxxx> 
>> >> > wrote:
>> >> Try to use HYPERVISOR_kexec_op() to find out where crash buffer is.
>> >> But it returned address that outside of total memory!
>> >
>> > Yes, because the Hyervisor (which is running below your dom0 Linux kernel)
>> > reserves the memory, so not even the dom0 kernel should be able to scribble
>> > it. That's why you have to use the HYPERVIROS_OPs.
>> >
>> > I've spend some time investigating this a month ago but finally did gave 
>> > up.
>> >
>> > Here're some of my notes:
>> > - it should be possible to write a user-space tool (like kexec), which uses
>> > HYPERVISOR_kexec_op() to load a crash-dump kernel.
>> > - you would need to copy some code from the linux-kernel to fill in some
>> > data
>> > structures.
>> > - the Linux kernel prepends the crash kernel with some assembly code, which
>> > moves it to the final location on execution. This trampolin code would
>> > possibly be Âneeded in your tool as well.
>> >
>> > The other option I see would be to modify the current Linux kernel to use
>> > HYPERVISOR_kexec_op() when used as a dom0 kernel.
>> You may want to get in touch with Daniel, who iirc started looking at
>> adding kexec support to the pv-ops kernel some time last year.
> ... and I still work on it. To be precise I have working kexec for
> domU PV guest running very ancient Linux Kernel Ver. 2.6.18 (it is
> not based on current 2.6.18 tree). I am starting work on kdump for domU.
> Work on kexec/kdump for dom0 is postponed until I finnish work on
> kexec/kdump for domU. After that I would like to prepare relevant patches
> for Xen, mainline Linux Kernel and kexec-tools and publish them as a complete
> solution for dom0 and domU (I am going to do that on March or April,
> however, ... You know...). I am not going to prepare support/backport for
> Linux Kernel Ver. 2.6.32 (or even 2.6.18), however, if it be required
> by quite large number of users I will think about that.
> Regarding kexec/kdump documentation please look into my presentation
> prepared for Xen Summit 2011 
> (http://xen.org/files/xensummit_santaclara11/aug3/7_DanielK_Kexec_KDump.pdf).
> I do not mention documentation which you could find in Linux Kernel source
> code. However, if you need some more explanation drop me a line.
> Daniel

At beginning, I though there are some hypervisor calls to find out the
crash buffer, put image into it, excute it. But it seems not.
I have to study kexec/kdump in both linux and xen to figure out how to
support kdump.

Thank you guys.


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