linux-kernel - Re: [PATCH 02/15] iommu: Introduce iommu domain types

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Date:	Fri, 30 Jan 2015 13:22:34 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Kukjin Kim <kgene@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	"linux-rockchip@...ts.infradead.org" 
	<linux-rockchip@...ts.infradead.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [PATCH 02/15] iommu: Introduce iommu domain types

Hi Will,

On Wed, Jan 28, 2015 at 02:19:34PM +0000, Will Deacon wrote:
> > +/* This are the possible domain-types */
> > +enum iommu_domain_type {
> > +	IOMMU_DOMAIN_DMA,	/* Domain used for DMA-API */
> > +	IOMMU_DOMAIN_IDENTITY,	/* Identity mapped domain  */
> 
> What happens if somebody calls map or unmap on an identity-mapping domain?
> Can we catch that in the IOMMU core before calling the IOMMU driver? That
> also implies we need something extra to parameterise the attributes for
> the mapping (e.g. cacheable, read-only) and also potentially the address
> range.

The domain type is only used by the IOMMU drivers to do be able to enter
special allocation paths (the AMD-Vi driver for example could allocate a
special internal domain type for IOMMU_DOMAIN_DMA).
But I think you are right, a couple of the current domain attributes we
have could be moved here, turning the domain-type into a bit-field. So
we could have bits for PAGING, CACHABLE, DMA_API and NESTING and build
the domain types above from those bits.

> > +	IOMMU_DOMAIN_UNMANAGED, /* Domain mappings are managed by a third party
> > +				   user (like KVM or VFIO) */
> 
> We already have the domain attributes (iommu_attr) to describe features
> of a domain. Is there really a need for this extra type, or can we extend
> the attribute set and allow for domain allocation with attributes?

I don't think that domains attributed will become obsolete with this
domain-type field. Some of the attributes should stay there for now,
like all the PAMU specific stuff. But I agree, some could be moved over.

	
	Joerg

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