linux-kernel - Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

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Date:	Mon, 12 Jul 2010 22:52:43 -0700
From:	Zach Pfeffer <zpfeffer@...eaurora.org>
To:	Joerg Roedel <joro@...tes.org>
CC:	Andi Kleen <andi@...stfloor.org>,
	Daniel Walker <dwalker@...eaurora.org>,
	Randy Dunlap <randy.dunlap@...cle.com>, mel@....ul.ie,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager

Joerg Roedel wrote:
> On Thu, Jul 01, 2010 at 11:17:34PM -0700, Zach Pfeffer wrote:
>> Andi Kleen wrote:
> 
>>> Hmm? dma_map_* does not change any CPU mappings. It only sets up
>>> DMA mapping(s).
>> Sure, but I was saying that iommu_map() doesn't just set up the IOMMU
>> mappings, its sets up both the iommu and kernel buffer mappings.
> 
> What do you mean by kernel buffer mappings?

In-kernel mappings whose addresses can be dereferenced. 

> 
> 
>>> That assumes that all the IOMMUs on the system support the same page table
>>> format, right?
>> Actually no. Since the VCMM abstracts a page-table as a Virtual
>> Contiguous Region (VCM) a VCM can be associated with any device,
>> regardless of their individual page table format.
> 
> The IOMMU-API abstracts a page-table as a domain which can also be
> associated with any device (behind an iommu).

It does, but only by convention. The domain member is just a big
catchall void *. It would be more useful to factor out a VCM
abstraction, with associated ops. As it stands all IOMMU device driver
writters have to re-invent IOMMU virtual address management.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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