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

[Avi Kivity]

On 06/01/2010 12:55 PM, Michael S. Tsirkin wrote:
> >   It can't program the iommu.
> > What
> > the patch proposes is that userspace tells vfio about the needed
> > mappings, and vfio programs the iommu.
> >      
> There seems to be some misunderstanding.  The userspace interface
> proposed forces a separate domain per device and forces userspace to
> repeat iommu programming for each device.  We are better off sharing a
> domain between devices and programming the iommu once.
>    

  iommufd = open(/dev/iommu);
  ioctl(iommufd, IOMMUFD_ASSIGN_RANGE, ...)
  ioctl(vfiofd, VFIO_SET_IOMMU, iommufd)

?

If so, I agree.

> The natural way to do this is to have an iommu driver for programming
> iommu.
>
> This likely means we will have to pass the domain to 'vfio' or uio or
> whatever the driver that gives userspace the access to device is called,
> but this is only for security, there's no need to support programming
> iommu there.
>
> And using this design means the uio framework changes
> required would be minor, so we won't have to duplicate code.
>    

Since vfio would be the only driver, there would be no duplication.  But 
a separate object for the iommu mapping is a good thing.  Perhaps we can 
even share it with vhost (without actually using the mmu, since vhost is 
software only).

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

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