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

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Message-ID: <20081201140711.GA12816@amd.com>
Date:	Mon, 1 Dec 2008 15:07:11 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Muli Ben-Yehuda <muli@...ibm.com>
CC:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, weidong.han@...el.com,
	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 03:02:09PM +0200, Muli Ben-Yehuda 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?

Yes, this can not be used for not-pv device passthrough. But I think it
can speed up the pvdma case. Beside that I can be used for UIO and
devices which perform bad with sg.

Joerg

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