linux-kernel - Re: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk

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Message-ID: <20140222121315.GB9012@e102568-lin.cambridge.arm.com>
Date:	Sat, 22 Feb 2014 12:13:15 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Sebastian Capella <sebastian.capella@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russ Dill <Russ.Dill@...com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Nicolas Pitre <nico@...aro.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Will Deacon <Will.Deacon@....com>,
	Cyril Chemparathy <cyril@...com>,
	Jonathan Austin <Jonathan.Austin@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH RFC v1 3/3] ARM hibernation / suspend-to-disk

On Sat, Feb 22, 2014 at 10:16:55AM +0000, Russell King - ARM Linux wrote:
> On Thu, Feb 20, 2014 at 04:27:55PM +0000, Lorenzo Pieralisi wrote:
> > I still do not understand why switching to idmap, which is a clone of
> > init_mm + 1:1 kernel mappings is required here. Why idmap ?
> > 
> > And while at it, can't the idmap be overwritten _while_ copying back the
> > resume kernel ? Is it safe to use idmap page tables while copying ?
> > 
> > I had a look at x86 and there idmap page tables used to resume are created
> > on the fly using safe pages, on ARM idmap is created at boot.
> 
> That's fine.
> 
> Remember, you're required to boot exactly the same kernel image when
> resuming as the kernel which created the suspend image.  Unless you
> have random allocations going on, you should get the same layout for
> the idmap stuff at each boot.

Thanks Russell, now that's clear. We do need a copy of page tables
that are not tampered with while copying, and idmap works well for
that.

Lorenzo

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