Re: [Qemu-devel] [RFC] Device isolation infrastructure v2

[Joerg Roedel <joerg.roedel@amd.com>]

On Thu, Dec 15, 2011 at 11:05:07AM -0700, Alex Williamson wrote:
> Starting with it in the core and hand waving some future use that we
> don't plan to implement right now seems like the wrong direction.

I agree with Alex. First of all, I havn't seen any real vfio problem
that can't be solved with the current approach, and it has the great
advantage of simplicity. It doesn't require a re-implementation of the
driver-core based on groups. I agree that we need some improvements to
Alex' code for the dma-api layer to solve the problem with broken devices
using the wrong requestor-id. But that can be done incrementally with
the current (current == in the iommu-tree) approach implemented by Alex.

I also think that all this does not belong into the driver core for two
reasons:

	1) The information for building the device groups is provided
	   by the iommu-layer
	2) The group information is provided to vfio by the iommu-api

This makes the iommu-layer the logical point to place the grouping code.
There are some sources outside of the iommu-layer that may influence
grouping (like pci-quirks), but most of the job is done by the
iommu-drivers.

Thanks,

	Joerg

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