linux-kernel - Re: [PATCH 3/9] add frontend implementation for the IOMMU API

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Message-ID: <20081201142727.GL29705@8bytes.org>
Date:	Mon, 1 Dec 2008 15:27:27 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	muli@...ibm.com, kvm@...r.kernel.org, weidong.han@...el.com,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	mingo@...hat.com, avi@...hat.com, amit.shah@...hat.com
Subject: Re: [PATCH 3/9] add frontend implementation for the IOMMU API

On Mon, Dec 01, 2008 at 11:18:39PM +0900, FUJITA Tomonori wrote:
> On Mon, 1 Dec 2008 15:02:09 +0200
> Muli Ben-Yehuda <muli@...ibm.com> wrote:
> 
> > On Mon, Dec 01, 2008 at 01:00:26PM +0100, Joerg Roedel wrote:
> > 
> > > > > > The majority of the names (include/linux/iommu.h, iommu.c,
> > > > > > iommu_ops, etc) looks too generic? We already have lots of
> > > > > > similar things (e.g. arch/{x86,ia64}/asm/iommu.h, several
> > > > > > archs' iommu.c, etc). Such names are expected to be used by
> > > > > > all the IOMMUs.
> > > > > 
> > > > > The API is already useful for more than KVM. I also plan to
> > > > > extend it to support more types of IOMMUs than VT-d and AMD
> > > > > IOMMU in the future. But these changes are more intrusive than
> > > > > this patchset and need more discussion. I prefer to do small
> > > > > steps into this direction.
> > > > 
> > > > Can you be more specific? What IOMMU could use this? For example,
> > > > how GART can use this? I think that people expect the name 'struct
> > > > iommu_ops' to be an abstract for all the IOMMUs (or the majority
> > > > at least). If this works like that, the name is a good choice, I
> > > > think.
> > > 
> > > GART can't use exactly this. But with some extensions we can make it
> > > useful for GART and GART-like IOMMUs too. For example we can emulate
> > > domains in GART by partitioning the GART aperture space.
> > 
> > That would only work with a pvdma API, since GART doesn't support
> > multiple address spaces, and you don't get the isolation properties of
> > a real IOMMU, so... why would you want to do that?
> 
> If this works for only IOMMUs that support kinda domain concept, then
> I think that a name like iommu_domain_ops is more appropriate.

Hmm, is there any hardware IOMMU with which we can't emulate domains by
partitioning the IO address space? This concept works for GART and
Calgary.

Joerg

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