linux-kernel - Re: [PATCH][v8] PM / hibernate: Verify the consistent of e820 memory map by md5 value

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Message-ID: <20160908211552.GA12651@amd>
Date:   Thu, 8 Sep 2016 23:15:52 +0200
From:   Pavel Machek <pavel@....cz>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     joeyli <jlee@...e.com>, Borislav Petkov <bp@...en8.de>,
        Chen Yu <yu.c.chen@...el.com>, linux-pm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Lee@...gul.tnic
Subject: Re: [PATCH][v8] PM / hibernate: Verify the consistent of e820 memory
 map by md5 value

On Tue 2016-08-30 13:54:44, Rafael J. Wysocki wrote:
> On Tuesday, August 30, 2016 04:35:05 PM joeyli wrote:
> > On Mon, Aug 29, 2016 at 03:41:23PM +0200, Borislav Petkov wrote:
> > > On Mon, Aug 29, 2016 at 09:15:00AM +0200, Pavel Machek wrote:
> > > > Sounds about as easy as hot unplugging arbitrary memory address. IOW
> > > > "not easy".
> > > 
> > > Regardless, forcibly panicking the system more is still the wrong
> > > approach IMO.
> > > 
> > > Instead, I'd try to issue a big fat warning that BIOS corrupts E820 and
> > > that the user should disable hibernation on that box and never ever
> > > enable it again.
> > > 
> > > After that, the kernel should *disable* hibernation for the current boot
> > > so any further hibernation runs don't even happen. Maybe even taint
> > > itself.
> > >
> > 
> > I support this idea to disable hibernation when kernel detected e820 layout
> > was changed by BIOS. If system resume luckily then kernel should warn to user
> > and refuse to hibernate again. User must to know that's better to reboot
> > system when he saw the warning message after lucky resume.
> > 
> > Not just BIOS doesn't fix e820 layout. There have some machines doesn't provide
> > _S4_ function, so the hibernation fallbacks to "shutdown" mode because "platform"
> > mode unavailable. In this situation, user is just lucky to run the hibernation.
> > Kernel should warn to user and disable hibernation when detected e820 layout
> > changed.
> 
> Well, please see my reply to Boris.
> 
> Pavel is right that running after detecting an e820 mismatch is generally risky,
> so why don't we shut down the system (but try to do that cleanly instead of
> causing it to panic right away) on an e820 mismatch?

I don't think that's good idea.

Anything involving userspace is risky at that point, and clean
shutdown means a _lot_ of userspace.

We know the filesystems are reasonably clean as we sync-ed
them; I believe right solution is to panic -- on-disk state is pretty
good and we don't want to do anything risky.

Best regards,

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