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Date:	Thu, 7 Aug 2014 16:52:03 +0800
From:	joeyli <jlee@...e.com>
To:	Pavel Machek <pavel@....cz>
Cc:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Takashi Iwai <tiwai@...e.de>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Hibernate: check unsafe page should not in e820
 reserved region

On Thu, Aug 07, 2014 at 10:00:25AM +0200, Pavel Machek wrote:
> Hi!
> 
> > > When the machine doesn't well handle the e820 persistent when hibernate
> > > resuming, then it may causes page fault when writing image to snapshot
> > > buffer:
> > > 
> > > [   17.929495] BUG: unable to handle kernel paging request at ffff880069d4f000
> > > [   17.933469] IP: [<ffffffff810a1cf0>] load_image_lzo+0x810/0xe40
> > > [   17.933469] PGD 2194067 PUD 77ffff067 PMD 2197067 PTE 0
> > > [   17.933469] Oops: 0002 [#1] SMP
[...]
> > > [    8.933534] PM: Failed to load hibernation image, recovering.
> > > 
> > > v2:
> > >  + removed empty check of nosave_regions list.
> > >  + fixed the typo of "region" in code for error message and patch comment.
> > > 
> > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > > Cc: Len Brown <len.brown@...el.com>
> > > Cc: Takashi Iwai <tiwai@...e.de>
> > > Acked-by: Pavel Machek <pavel@....cz>
> > > Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> > 
> > I discussed with Vojtech Pavlik for this patch, he raised a situation is:
> > 
> > Maybe e820 changed but image kernel original pages do not fall into new e820 region.
> > Then the hibernate will recovery success, but later kernel drivers may got problem
> > when accessing memory. 
> > 
> > My idea is hashing the start/end pfn of each nosave region sequentially, put this
> > nosave region digest to hibernate header then compare e820 digest in check_header()
> > when hibernate resuming.
> > 
> > I am developing patch, then we don't need check unsafe page should not in unsave(e820)
> > regions.
> 
> Actually, if you are doing such a check... it makes sense to check for
> _all_ the regions, nosave or not. If e820 map changed at all, it is
> not safe to resume.
> 									Pavel

Currently nosave region only called register by e820 code, so hibernate's nosave region included e820
reserved, ACPI data and ACPI NVS region.

I thought hashing the start/end pfn of above regions is enough.


Regards
Joey Lee
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