linux-kernel - Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

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Message-ID: <20100530124949.GI27611@redhat.com>
Date:	Sun, 30 May 2010 15:49:49 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Tom Lyon <pugs@...co.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, chrisw@...s-sol.org, joro@...tes.org,
	hjk@...utronix.de, gregkh@...e.de, aafabbri@...co.com,
	scofeldm@...co.com
Subject: Re: [PATCH] VFIO driver: Non-privileged user level PCI drivers

On Sun, May 30, 2010 at 03:27:05PM +0300, Avi Kivity wrote:
> 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<pugs@...co.com>
>>> ---
>>> 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.

Force assigning to iommu before we allow any other operation?

>>> [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  
> iommu.

Yes but userspace can do this. As long as userspace can not
crash the kernel, no reason to put this policy into kernel.

>
> -- 
> error compiling committee.c: too many arguments to function
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