linux-kernel - Re: [linux-pm] Re: Hibernation considerations

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Message-ID: <Pine.LNX.4.64.0707200845200.19248@asgard.lang.hm>
Date:	Fri, 20 Jul 2007 08:48:52 -0700 (PDT)
From:	david@...g.hm
To:	"Huang, Ying" <ying.huang@...el.com>
cc:	Milton Miller <miltonm@....com>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J.Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Jeremy Maitin-Shepard <jbms@....edu>
Subject: Re: [linux-pm] Re: Hibernation considerations

On Fri, 20 Jul 2007, Huang, Ying wrote:

> 
> On Fri, 2007-07-20 at 09:01 -0500, Milton Miller wrote:
>> Simplifying kjump: the proposal for v3.
>>
>> The current code is trying to use crash dump area as a safe, reserved
>> area to run the second kernel.   However, that means that the kernel
>> has to be linked specially to run in the reserved area.   I think we
>> need to finish separating kexec_jump from the other code paths.
>>
>> (1) add a new command line argument that specifies the kexec_jump
>> target area (or just size?)
>>
>> (2) add a kjump flag to the flags parameter, used by kexec_load.   When
>> loading a jump kernel, it is loaded like a normal kernel, however,
>> additional control pages are allocated to (a) save this kenrel's use of
>> the kexec_jump target area (b) save the backed up region that is used
>> by all kernels like crash dump, and (c) space for invoking
>> relocate_new_kernel that will get its args from the execution entry
>> point and will restore the kernel then call resume and suspend.
>
> Backuping target memory before kexec and restoring it after kexec is
> planed feature for kexec jump. But I will work on image writing/reading
> first.

if we can get a list of what memory is safe to backup/restore then the 
reading/writing of the image should be able to be done in userspace.

>> (3) replace jump_huf_pfn with two command line addresses that specify
>> the (a) return point for after resume, and (b) the return point for
>> after image save.   Actually these can be done in userspace; the second
>> restore kernel can just specify the null copy list and the entry points
>> supplied by the suspended kernel.  To do resume we also need (c) where
>> to store resume address for the save kernel.
>
> There is many free spaces in jump_buf_pfn page now. I think passing the
> needed information through jump_buf_pfn is more convenient than through
> kernel command line. That is, the jump_buf_pfn can be seen as a meta
> interface, which is passed to kexeced kernel though command line, while
> other information can be passed though jmp_buf_pfn.



>> The seperation should be whoever builds a scatter copy list builds the
>> inverse list.  This is why I propose simple jump entry points.  I
>> expect just a few instructions to establish arguments for the call to
>> the exstinging relocate_new_kernel code.
>
> If the "scatter copy" is replaced by "scatter swap", we need not the
> inverse list, and the state of kexeced kernel can be backuped too. There
> are "scatter copy" support in normal kexec implementation in
> "relocate_kernel".

what do you mean by "scatter swap"?

David Lang
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