linux-kernel - Re: [PATCH] Hibernation: Document __save_processor

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Message-Id: <200712311857.34445.rjw@sisk.pl>
Date:	Mon, 31 Dec 2007 18:57:33 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH] Hibernation: Document __save_processor_state() on x86-64

On Monday, 31 of December 2007, Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@...k.pl> wrote:
> 
> > > ok, just to make sure we are talking about the same thing. Do you 
> > > mean we can restore an image saved by v2.6.12 into v2.6.24? I.e. a 
> > > 2.6.24 kernel will be able to run a 2.6.12 kernel's hibernation 
> > > image, with all the kernel internal data from v2.6.12, etc? No way 
> > > can that work.
> > 
> > Well, not exactly.  The support for different boot and image kernels 
> > has only been merged recently, but we can use the current git to 
> > restore 2.6.24-rc6-mm1, for example.
> > 
> > The trick is to pass a little additional information in the image 
> > header that can be used by the boot kernel to locate the entry point 
> > to the image kernel and the image kernel's page tables.
> 
> ok - i thought you meant that there's a general capability to resume 
> across kernel versions. (which would be close to impossible without some 
> major surgery.)

Well, there will be one. :-)  For example, one should be able to use a 2.6.25+
boot kernel to load the image containing 2.6.24-rc6 and restore the memory
state from it.

> btw., in what way is this different from kexec?

Not that much different indeed.  The hibernation code is more focused on
restoring the pre-hibernation state of the system rather than anything else,
plus on ACPI systems we try to handle the platform in accordance with the
specification (to some extent - you'd have to use a non-ACPI boot kernel to
follow the specification literally, which is possible but not straightforward).

Rafael
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