linux-kernel - RE: [PATCHv8 00/12] Contiguous Memory Allocator

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Date:	Thu, 23 Dec 2010 11:58:08 +0100
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Russell King - ARM Linux' <linux@....linux.org.uk>,
	'Kyungmin Park' <kmpark@...radead.org>
Cc:	'Michal Nazarewicz' <m.nazarewicz@...sung.com>,
	linux-arm-kernel@...ts.infradead.org,
	'Daniel Walker' <dwalker@...eaurora.org>,
	'Johan MOSSBERG' <johan.xx.mossberg@...ricsson.com>,
	'Mel Gorman' <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	'Michal Nazarewicz' <mina86@...a86.com>, linux-mm@...ck.org,
	'Ankita Garg' <ankita@...ibm.com>,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	linux-media@...r.kernel.org,
	'KAMEZAWA Hiroyuki' <kamezawa.hiroyu@...fujitsu.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: RE: [PATCHv8 00/12] Contiguous Memory Allocator

Hello,

On Thursday, December 23, 2010 11:07 AM Russell King - ARM Linux wrote:

> On Thu, Dec 23, 2010 at 06:30:57PM +0900, Kyungmin Park wrote:
> > Hi Andrew,
> >
> > any comments? what's the next step to merge it for 2.6.38 kernel. we
> > want to use this feature at mainline kernel.
> 
> Has anyone addressed my issue with it that this is wide-open for
> abuse by allocating large chunks of memory, and then remapping
> them in some way with different attributes, thereby violating the
> ARM architecture specification?

Actually this contiguous memory allocator is a better replacement for
alloc_pages() which is used by dma_alloc_coherent(). It is a generic
framework that is not tied only to ARM architecture.

> In other words, do we _actually_ have a use for this which doesn't
> involve doing something like allocating 32MB of memory from it,
> remapping it so that it's DMA coherent, and then performing DMA
> on the resulting buffer?

This is an arm specific problem, also related to dma_alloc_coherent()
allocator. To be 100% conformant with ARM specification we would
probably need to unmap all pages used by the dma_coherent allocator
from the LOW MEM area. This is doable, but completely not related
to the CMA and this patch series.

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center


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