linux-kernel - Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

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Date:	Tue, 19 Oct 2010 20:21:32 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Colin Cross <ccross@...gle.com>
Cc:	Felipe Contreras <felipe.contreras@...il.com>,
	Greg KH <greg@...ah.com>,
	linux-main <linux-kernel@...r.kernel.org>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Arnd Hannemann <arnd@...dnet.de>,
	Han Jonghun <jonghun79.han@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Hemant Pedanekar <hemantp@...com>
Subject: Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM

On Tue, Oct 19, 2010 at 01:13:36AM -0700, Colin Cross wrote:
> On Mon, Oct 11, 2010 at 8:25 AM, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Sun, Oct 10, 2010 at 04:52:36AM +0300, Felipe Contreras wrote:
> > Here's a different approach which will work.  This pushes ARM further
> > towards using memblock for everything relating to memory init (although
> > we still have the old membank stuff around.)
> >
> > The advantage with this is that memblock is now used as the basis for
> > determining where memory is, setting up the maps, freeing memory into
> > the pools, etc.
> >
> > What this also means is that this code in the ->reserve callback:
> >
> >        size = min(size, SZ_2M);
> >        base = memblock_alloc(size, min(align, SZ_2M));
> >        memblock_free(base, size);
> >        memblock_remove(base, size);
> >
> > will result in [base+size] being removed from the available memory,
> > using highmem if available, if not from lowmem and removing it from
> > the lowmem memory map - which is exactly the behaviour we want.
> >
> >  arch/arm/mm/init.c |  160 +++++++++++++++++++++++++++++++++++-----------------
> >  arch/arm/mm/mmu.c  |   43 ++++++++------
> >  mm/memblock.c      |    4 +
> >  3 files changed, 138 insertions(+), 69 deletions(-)
> 
> If memblock_remove is used on the end of memory with this patch,
> mem_init accesses off the end of the array of page structures because
> of the discrepancy between memblock.memory and membank on the number
> of the last pfn.   memblock.memory is used to determine the memory
> zones in arm_bootmem_free, which eventually  is used to create the
> array of page structures, but mem_init iterates over membank and calls
> pfn_to_page on pfns up to bank_pfn_end.

BTW, reverting the change to find_limits() should resolve this problem.
Please confirm.
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