linux-kernel - Re: [PATCH 0/9][RFC] stackable dma

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Message-ID: <20080928184926.GB26563@8bytes.org>
Date:	Sun, 28 Sep 2008 20:49:26 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	joerg.roedel@....com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, iommu@...ts.linux-foundation.org,
	dwmw2@...radead.org, muli@...ibm.com, amit.shah@...ranet.com,
	mingo@...hat.com
Subject: Re: [PATCH 0/9][RFC] stackable dma_ops for x86

On Sun, Sep 28, 2008 at 11:21:26PM +0900, FUJITA Tomonori wrote:
> On Mon, 22 Sep 2008 20:21:12 +0200
> Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > Hi,
> > 
> > this patch series implements stackable dma_ops on x86. This is useful to
> > be able to fall back to a different dma_ops implementation if one can
> > not handle a particular device (as necessary for example with
> > paravirtualized device passthrough or if a hardware IOMMU only handles a
> > subset of available devices).
> 
> We already handle the latter. This patchset is more flexible but
> seems to incur more overheads.
> 
> This feature will be used for only paravirtualized device passthrough?
> If so, I feel that there is more simpler (and specific) solutions for
> it.

Its not only for device passthrough. It handles also the cases where a
hardware IOMMU does not handle all devices in the system (like in some
Calgary systems but also possible with AMD IOMMU). With this patchset we
can handle these cases in a generic way without hacking it into the
hardware drivers (these hacks are also in the AMD IOMMU code and I plan
to remove them in the case this patchset will be accepted).

Joerg

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