linux-kernel - Re: [PATCH] iommu: Include MSI susceptibility to DMA in creating iommu groups

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Message-ID: <20111121233505.GG3344@sequoia.sous-sol.org>
Date:	Mon, 21 Nov 2011 15:35:05 -0800
From:	Chris Wright <chrisw@...s-sol.org>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] iommu: Include MSI susceptibility to DMA in creating
 iommu groups

* Joerg Roedel (joro@...tes.org) wrote:
> >From device standpoint a MSI transaction is always a DMA memory write
> to a given address range. The IOMMU-API should export a feature flag
> whether it supports filtering on those transaction or not. We have that
> today with the IOMMU_CAP_INTR_REMAP. I agree that the interface to get
> this information is ugly because a domain is needed. But the interface
> can be fixed. While doing this I suggest to rename that feature
> IOMMU_CAP_INTR_ISOLATION or something like that.
> VFIO can then check for this flag on module-load and refuse to load if
> it is not available.

I can see that the native grouping (the typical pci bridge type) is
really more a property of the topology.

The isolation properties of a group (arguably the whole point of the
group) is subtly different.

Leaves the questions:

What is the value of a group w/out complete isolation?
Is there a practical problem w/ conflating the subtleties above?

thanks,
-chris
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