linux-kernel - Re: [PATCH 8/8] iommu: Move default domain allocation to iommu_group_get_for

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Date:	Fri, 30 Oct 2015 15:13:47 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Will Deacon <will.deacon@....com>
Cc:	iommu@...ts.linux-foundation.org,
	Alex Williamson <alex.williamson@...hat.com>,
	linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 8/8] iommu: Move default domain allocation to
 iommu_group_get_for_dev()

Hi Will,

On Thu, Oct 29, 2015 at 06:22:49PM +0000, Will Deacon wrote:
> The call to iommu_group_get_for_dev in arm_smmu_add_device will end up
> calling __iommu_attach_device, since group->domain will now be initialised
> by the code above. This means the SMMU driver will see an ->attach_dev
> call for a device that is part-way through an ->add_device callback and
> will be missing the initialisation necessary for us to idenfity the SMMU
> instance to which is corresponds. In fact, the iommudata for the group
> won't be initialised at all, so the whole thing will fail afaict.
> 
> Note that I haven't actually taken this for a spin, so I could be missing
> something.

Yeah, I havn't looked at how to convert the ARM-SMMU drivers to default
domains yet, so the issue you describe above is totally possible.

But there is no way to trigger it yet, because your domain_alloc
function can not yet allocate IOMMU_DOMAIN_DMA domains. While converting
the issue must be fixed, of course.

I tested this patch-set on an AMD Seattle system and it worked fine
there.


	Joerg

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