linux-kernel - Re: [PATCH 1/4 -mm] kexec based hibernation -v7 : kexec jump

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Message-ID: <20071208235344.GA17005@elf.ucw.cz>
Date:	Sun, 9 Dec 2007 00:53:44 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	nigel@...el.suspend2.net, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH 1/4 -mm] kexec based hibernation -v7 : kexec jump

Hi!

> This patch implements the functionality of jumping between the kexeced
> kernel and the original kernel.
> 
> To support jumping between two kernels, before jumping to (executing)
> the new kernel and jumping back to the original kernel, the devices
> are put into quiescent state, and the state of devices and CPU is
> saved. After jumping back from kexeced kernel and jumping to the new
> kernel, the state of devices and CPU are restored accordingly. The
> devices/CPU state save/restore code of software suspend is called to
> implement corresponding function.
> 
> To support jumping without reserving memory. One shadow backup page
> (source page) is allocated for each page used by new (kexeced) kernel
> (destination page). When do kexec_load, the image of new kernel is
> loaded into source pages, and before executing, the destination pages
> and the source pages are swapped, so the contents of destination pages
> are backupped. Before jumping to the new (kexeced) kernel and after
> jumping back to the original kernel, the destination pages and the
> source pages are swapped too.
> 
> A jump back protocol for kexec is defined and documented. It is an
> extension to ordinary function calling protocol. So, the facility
> provided by this patch can be used to call ordinary C function in real
> mode.
> 
> A set of flags for sys_kexec_load are added to control which state are
> saved/restored before/after real mode code executing. For example, you
> can specify the device state and FPU state are saved/restored
> before/after real mode code executing.
> 
> The states (exclude CPU state) save/restore code can be overridden
> based on the "command" parameter of kexec jump. Because more states
> need to be saved/restored by hibernating/resuming.
> 
> Signed-off-by: Huang Ying <ying.huang@...el.com>

I'm not kexec hacker... but maybe this is in good enough state to be
merged? It is useful on its own: kexec jump and back means we can dump
system then continue running, for example...

								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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