How to test preserve_context mode?

[Dave Young]

Hi David,

I did not see anyone around me test this.   The kexec jump feature was
introduced by Ying [cced him] in below kernel comment, probably you
can try the steps mentioned in the commit log:
commit 3ab83521378268044a448113c6aa9a9e245f4d2f
Author: Huang Ying <ying.huang at intel.com>
Date:   Fri Jul 25 19:45:07 2008 -0700

    kexec jump

On Fri, 15 Nov 2024 at 19:15, David Woodhouse <dwmw2 at infradead.org> wrote:
>
> I'm messing around with the x86 relocate_kernel code, and I'd like to
> test the 'preserve_context' mode. I can't find any documentation or
> examples; am I just being dim?
>
> All I want to do is kexec into an environment which just does a 'ret',
> and comes back to the original kernel.
>
> I've only been able to do that by hacking out the 'call %rdx' in
> relocate_kernel_64.S so it never even calls into the environment in the
> first place.
>
> (Which doesn't work, as the kernel forgets to reload its own GDT, but
> with *that* fixed it seems fine.)
>
>
>
> Also, I've configured the mailing list to no longer append a footer,
> because it makes the lore.kernel.org archive unhappy.

Thanks
Dave