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

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Date:	Mon, 1 Dec 2008 13:00:26 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	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 05:38:11PM +0900, FUJITA Tomonori wrote:
> On Fri, 28 Nov 2008 12:31:29 +0100
> Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > On Fri, Nov 28, 2008 at 06:40:41PM +0900, FUJITA Tomonori wrote:
> > > On Thu, 27 Nov 2008 16:40:48 +0100
> > > Joerg Roedel <joerg.roedel@....com> wrote:
> > > 
> > > > Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> > > > ---
> > > >  drivers/base/iommu.c |   94 ++++++++++++++++++++++++++++++++++++++++++++++++++
> > > >  1 files changed, 94 insertions(+), 0 deletions(-)
> > > >  create mode 100644 drivers/base/iommu.c
> > > > 
> > > > diff --git a/drivers/base/iommu.c b/drivers/base/iommu.c
> > > > new file mode 100644
> > > > index 0000000..7250b9c
> > > > --- /dev/null
> > > > +++ b/drivers/base/iommu.c
> > > 
> > > Hmm, why is this at drivers/base/? Anyone except for kvm could use
> > > this? If so, under virt/ is more appropriate?
> > 
> > I don't see a reason why this should be KVM specific. KVM is the only
> > user for now. But it can be used for i.e. UIO too. Or in drivers to
> > speed up devices which have bad performance when they do scather gather
> > IO.
> 
> If there are some except for kvm that could use this, it should be
> fine, I guess.
> 
> Can you add such information (e.g. who could use this) to the patch
> description? It should be in the git log if the patch is merged.

Ok, I will add it.

> > > 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.

Joerg

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