linux-kernel - RE: [PATCH] [v4] PM / hibernate: Fix hibernation panic caused by inconsistent e820 map

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Date:	Fri, 18 Sep 2015 06:11:36 +0000
From:	"Chen, Yu C" <yu.c.chen@...el.com>
To:	Pavel Machek <pavel@....cz>
CC:	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"Brown, Len" <len.brown@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Zhang, Rui" <rui.zhang@...el.com>,
	"jlee@...e.com" <jlee@...e.com>,
	"joeyli.kernel@...il.com" <joeyli.kernel@...il.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: RE: [PATCH] [v4] PM / hibernate: Fix hibernation panic caused by
 inconsistent e820 map


Hi, Pavel,

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@....cz]
> Sent: Friday, September 18, 2015 1:47 PM
> To: Chen, Yu C
> Cc: rjw@...ysocki.net; Brown, Len; linux-pm@...r.kernel.org; linux-
> kernel@...r.kernel.org; Zhang, Rui; jlee@...e.com;
> joeyli.kernel@...il.com; yinghai@...nel.org; Ingo Molnar
> Subject: Re: [PATCH] [v4] PM / hibernate: Fix hibernation panic caused by
> inconsistent e820 map
> 
> > > 3) I'm not sure I understand the changelog correctly. What happens
> > > when BIOS reports less memory on hibernation? Will you magically
> > > remove memory from kernel at runtime? Will /proc/meminfo be invalid
> after resume?
> > > Will all the memory management tuning need fixing?
> > >
> > Oh, I did not notice it before. So deleting the logic of '
> > info->num_physpages != get_num_physpages()' is not suitable.
> > The subset relationship should not be considered in this patch.
> 
> Ok. So... if you really want, you can add some messages like "hey, this is bios
> bug, maybe updating bios is a good idea".. but please lets keep the original
> logic.
> 
OK. I see, I'll not change its original code.
So can I add a function here that checks if current BIOS  e820 map is 
strictly the same as it was before S4?  If it is not the same, we will print some warnnings
, and if we panic later, we will print that , the panic reason might be due to broken BIOS.
I think I can archive this by putting  the e820_saved array  into struct swsusp_info, 
 and pass it to second kernel: 
struct swsusp_info will always occupy one page size, and has a lot of extra space left,
meanwhile the total size of e820 map will not exceed the PAGE_SIZE currently, it's safe 
to put it in struct swsusp_info.

And this does not need much changing of current code. What do you think? Thanks.

Best Regards,
Yu



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