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

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Message-ID: <20101019181249.GA9789@n2100.arm.linux.org.uk>
Date:	Tue, 19 Oct 2010 19:12:49 +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:
> 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.
> 
> Converting show_mem and mem_init to use memblock.memory fixes it:

I intentionally did not do this because it won't work.  membank
information is purposely not coalesced together when you have full
sparsemem regions - which may result in

	pfn_to_page(pfn) != pfn_to_page(pfn + 1) - 1

However, memblock information is coalesced, and so will cross these
boundaries.  This means using memblock instead of membank will make
things go pop.
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