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

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Date:   Fri, 9 Sep 2016 09:33:50 +0200
From:   Pavel Machek <pavel@....cz>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, joeyli <jlee@...e.com>,
        Borislav Petkov <bp@...en8.de>, 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 Fri 2016-09-09 15:36:42, Chen Yu wrote:
> Hi Pavel,
> On Thu, Sep 08, 2016 at 11:15:52PM +0200, Pavel Machek wrote:
> > 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.
> >
> OK, we tried a milder solution that doesn't shutdown the system in the
> latest version, which terminates the restore process if a mismatch is found
> (hope people would be happy with that one :)

Actually, terminating the restore process is fine. Restoring into the
old state with different memory map and then attempting to shut down
would not be.

Best regards,
									Pavel

-- 
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