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

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Message-Id: <20080515184126O.tomof@acm.org>
Date:	Thu, 15 May 2008 18:41:26 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	andi@...stfloor.org
Cc:	fujita.tomonori@....ntt.co.jp, 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

On Thu, 15 May 2008 11:30:12 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> 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.

Thanks,

I thought that KVM people want to do it per device (in the first
case). So with my patchse, they can replace the dma_ops pointer in
dev_archdata with what they want.
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