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Date:	Sun, 30 May 2010 15:27:05 +0300
From:	Avi Kivity <>
To:	"Michael S. Tsirkin" <>
CC:	Tom Lyon <>,,,,,,,,
Subject: Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

On 05/30/2010 03:19 PM, Michael S. Tsirkin wrote:
> On Fri, May 28, 2010 at 04:07:38PM -0700, Tom Lyon wrote:
>> The VFIO "driver" is used to allow privileged AND non-privileged processes to
>> implement user-level device drivers for any well-behaved PCI, PCI-X, and PCIe
>> devices.
>> 	Signed-off-by: Tom Lyon<>
>> ---
>> This patch is the evolution of code which was first proposed as a patch to
>> uio/uio_pci_generic, then as a more generic uio patch. Now it is taken entirely
>> out of the uio framework, and things seem much cleaner. Of course, there is
>> a lot of functional overlap with uio, but the previous version just seemed
>> like a giant mode switch in the uio code that did not lead to clarity for
>> either the new or old code.
> IMO this was because this driver does two things: programming iommu and
> handling interrupts. uio does interrupt handling.
> We could have moved iommu / DMA programming to
> a separate driver, and have uio work with it.
> This would solve limitation of the current driver
> that is needs an iommu domain per device.

How do we enforce security then?  We need to ensure that unprivileged 
users can only use the device with an iommu.

>> [a pony for avi...]
>> The major new functionality in this version is the ability to deal with
>> PCI config space accesses (through read&  write calls) - but includes table
>> driven code to determine whats safe to write and what is not.
> I don't really see why this is helpful: a driver written corrrectly
> will not access these addresses, and we need an iommu anyway to protect
> us against a drivers.

Haven't reviewed the code (yet) but things like the BARs, MSI, and 
interrupt disable need to be protected from the guest regardless of the 

error compiling committee.c: too many arguments to function

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