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

From: ebiederm@xmission.com (Eric W. Biederman)
To: "Huang, Ying" <ying.huang@intel.com>
Cc: nigel@nigel.suspend2.net,
	Kexec Mailing List <kexec@lists.infradead.org>,
	linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
	Pavel Machek <pavel@ucw.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH] kexec based hibernation: a prototype of kexec multi-stage load
Date: Thu, 15 May 2008 20:33:41 -0700	[thread overview]
Message-ID: <m1iqxegbxm.fsf@frodo.ebiederm.org> (raw)
In-Reply-To: <1210906575.23707.189.camel@caritas-dev.intel.com> (Ying Huang's message of "Fri, 16 May 2008 10:56:15 +0800")

"Huang, Ying" <ying.huang@intel.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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