linux-kernel - Re: [PATCH 0/2] x86: per-device dma_mapping

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Message-ID: <482C02A4.80101@firstfloor.org>
Date:	Thu, 15 May 2008 11:30:12 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	muli@...ibm.com, alexisb@...ibm.com
Subject: Re: [PATCH 0/2] x86: per-device dma_mapping_ops

FUJITA Tomonori wrote:
> On Thu, 15 May 2008 11:01:09 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
>> FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> writes:
>>
>>> This patchset adds per-device dma_mapping_ops support for
>>> CONFIG_X86_64 like POWER architecture does. This change enables us to
>>> cleanly fix the Calgary IOMMU issue that some devices are not behind
>>> the IOMMU [1]. It also would be helpful to handle KVM PCI passthrough.
>> This makes it basically impossible to do stack ops, which some 
>> people have been doing.
> 
> Seems that I misunderstand what those people want.
> 
> What those people want to do and how the stack ops achieve it? Or can
> you tell me where their patches are?

I've seen it in two cases: first was for KVM IO bypass and the other was a 
(unfinished) patch to support the NoDMA bitmaps on some systems.

In this case you really want to do a wrapper around the existing ops
and extend the mapping. 

That worked fine by just replacing the global pointer, but will
be quite hard in your set up.

-Andi


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