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

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Message-ID: <20140222101655.GE21483@n2100.arm.linux.org.uk>
Date:	Sat, 22 Feb 2014 10:16:55 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
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 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.

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