linux-kernel - Re: [RFC] Device isolation infrastructure v2

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Date:	Fri, 16 Dec 2011 15:53:53 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	David Gibson <david@...son.dropbear.id.au>, <aik@...abs.ru>,
	<benh@...nel.crashing.org>, <dwmw2@...radead.org>,
	<chrisw@...hat.com>, <agraf@...e.de>, <scottwood@...escale.com>,
	<B08248@...escale.com>, <rusty@...tcorp.com.au>,
	<iommu@...ts.linux-foundation.org>, <qemu-devel@...gnu.org>,
	<linux-kernel@...r.kernel.org>, <joro@...tes.org>
Subject: Re: [RFC] Device isolation infrastructure v2

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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