On Tue, Feb 13, 2018 at 8:52 PM, Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx> wrote: > Jumping between the system kernel and the dump-capture kernel > has been supported for long time but there is no description > how to use it. This patch adds the description how to use kexec tool > to jump to the dump-capture kernel and jump back to the system kernel. > > Signed-off-by: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx> > --- > Documentation/kdump/kdump.txt | 38 ++++++++++++++++++++++++++++++++++++++ > 1 file changed, 38 insertions(+) > > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt > index 51814450a7f8..35b71fef5d88 100644 > --- a/Documentation/kdump/kdump.txt > +++ b/Documentation/kdump/kdump.txt > @@ -460,6 +460,44 @@ and the system will boot into the dump-capture kernel. > For testing purposes, you can trigger a crash by using "ALT-SysRq-c", > "echo c > /proc/sysrq-trigger" or write a module to force the panic. > > +Jump between the System kernel and the Dump-capture kernel > +=============================== > + > +Without system crash, the system can jump to the dump-capture kernel. > + > +1) Enable "jump between system kernel and dump-capture kernel" support under > + "Processor type and features" > + > + CONFIG_KEXEC_JUMP=y > + > +2) Load the dump-capture kernel with --load-preserve-context and mem-max > + options as following. > + > + kexec -l <dump-capture-kernel-vmlinux-image> \ > + --initrd=<initrd-for-dump-capture-kernel> --args-linux \ > + --append="root=<root-dev> <arch-specific-options>" \ > + --load-preserve-context \ > + --mem-max=<the highest memory address addr to load code into> > + > +3) Jump to the loaded kernel > + > + kexec -e > + > +Now the system is running with the dump-capture kernel. You can jump back > +to the system kernel. > + > +1) Find kexec_jump_back_entry address in kernel booting parameters in > + /proc/cmdline. That is the address for kexec to jump to. For example: > + kexec_jump_back_entry=0x00000000000810d2 > + > +2) Following command sets the jump-back address for kexec. > + > + kexec --load-jump-back-helper --entry=0x810d2 > + > +3) Jump to the system kernel > + > + kexec -e > + This is essentially the 'kexec -l' use case, i.e we are loading another kernel and not the kexec -p (or the conventional kdump) use case and description. I remember not being able to use the kexec -p (kdump feature) with the jump/preserve primary kernel attributes case previously, but that was some time back and haven't tried the same recently. So I am not sure if the kexec -p case works well with the jump feature currently, but I can try to setup an environment at my end. So I don't think that the kdump kernel documentation is the right place for this addition (as in this kernel document we essentially capture the 'kexec -p' or kdump case and not the 'kexec -l'). Rather we should add it the kexec man page (inside kexec-tools). See <git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git> for the man page. And I agree that this is a useful piece of documentation as I have burnt my hands while experimenting with the jump feature previously and I think it would be great to have this included somewhere in the kexec man page for ready reference. Regards, Bhupesh > Write Out the Dump File > ======================= > > -- > 2.11.0 > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
