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

[Daniel Kiper <dkiper@xxxxxxxxxxxx>]

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  needed 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

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