linux-kernel - Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load

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Message-ID: <m1iqxegbxm.fsf@frodo.ebiederm.org>
Date:	Thu, 15 May 2008 20:33:41 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Pavel Machek <pavel@....cz>,
	nigel@...el.suspend2.net, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load

"Huang, Ying" <ying.huang@...el.com> writes:


> I think it is reasonable to enable jumping back and forth more than one
> time.

I'm not opposed.  I just don't understand the utility yet.

> So the following should be possible:
>
> 1. Jump from A to B (actually jump to purgatory, trigger the boot of B)
> 2. Jump from B to A
> 3. Jump from A to B again (jump to the kexec_jump_back_entry of B)
                      (And we go through purgatory which remembers
                       the kexec_jump_back_entry of B)
> 4. Jump from B to A
> ...
>
> So it should be possible to get the re-entry point of kernel B in
> kexec_jump_back_entry of kernel A too. So I think in
> kexec_jump_back_entry, the caller's stack should be checked to get
> re-entry point of peer. And the stack state is different depend on where
> come from, from relocate_new_kernel() or return.

Yes.

Any conditional logic needs to be in purgatory or a similar trampoline.

Eric
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