Re: [Qemu-devel] [PATCH v2 09/13] vfio: x86 IOMMU implementation

[Don Dutile]

On 05/24/2012 06:46 PM, Alex Williamson wrote:
> On Thu, 2012-05-24 at 17:38 -0400, Don Dutile wrote:
> > On 05/22/2012 01:05 AM, Alex Williamson wrote:
> > > x86 is probably the wrong name for this VFIO IOMMU driver, but x86
> > > is the primary target for it.  This driver support a very simple
> > > usage model using the existing IOMMU API.  The IOMMU is expected to
> > > support the full host address space with no special IOVA windows,
> > > number of mappings restrictions, or unique processor target options.
> > >
> > > Signed-off-by: Alex Williamson<address@hidden>
> > > ---
> > >
> > >    Documentation/ioctl/ioctl-number.txt |    2
> > >    drivers/vfio/Kconfig                 |    6
> > >    drivers/vfio/Makefile                |    2
> > >    drivers/vfio/vfio.c                  |    7
> > >    drivers/vfio/vfio_iommu_x86.c        |  743 
> > > ++++++++++++++++++++++++++++++++++
> > >    include/linux/vfio.h                 |   52 ++
> > >    6 files changed, 811 insertions(+), 1 deletions(-)
> > >    create mode 100644 drivers/vfio/vfio_iommu_x86.c
> > >
> > > diff --git a/Documentation/ioctl/ioctl-number.txt 
> > > b/Documentation/ioctl/ioctl-number.txt
> > > index 111e30a..9d1694e 100644
> > > --- a/Documentation/ioctl/ioctl-number.txt
> > > +++ b/Documentation/ioctl/ioctl-number.txt
> > > @@ -88,7 +88,7 @@ Code  Seq#(hex)       Include File            Comments
> > >                 and kernel/power/user.c
> > >    '8'  all                             SNP8023 advanced NIC card
> > >                                         <mailto:address@hidden>
> > > -';'    64-6F   linux/vfio.h
> > > +';'    64-72   linux/vfio.h
> > >    '@'  00-0F   linux/radeonfb.h        conflict!
> > >    '@'  00-0F   drivers/video/aty/aty128fb.c    conflict!
> > >    'A'  00-1F   linux/apm_bios.h        conflict!
> > > diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
> > > index 9acb1e7..bd88a30 100644
> > > --- a/drivers/vfio/Kconfig
> > > +++ b/drivers/vfio/Kconfig
> > > @@ -1,6 +1,12 @@
> > > +config VFIO_IOMMU_X86
> > > +       tristate
> > > +       depends on VFIO&&   X86
> > > +       default n
> > > +
> > >    menuconfig VFIO
> > >         tristate "VFIO Non-Privileged userspace driver framework"
> > >         depends on IOMMU_API
> > > +       select VFIO_IOMMU_X86 if X86
> > >         help
> > >           VFIO provides a framework for secure userspace device drivers.
> > >           See Documentation/vfio.txt for more details.
> >
> > So a future refactoring that uses some chunk of this support
> > on a non-x86 machine could be a lot of useless renaming.
> >
> > Why not rename vfio_iommu_x86 to something like vfio_iommu_no_iova
> > and just make it conditionally compiled on X86 (as you've done above in 
> > Kconfig's)?
> > Then if another arch can use it, or refactors the file to use
> > some of it, and split x86 vs<other-arch>  into separate per-arch files,
> > or per-iova schemes, it's more descriptive and less disruptive?
>
> Yep, the problem is how to concisely describe what we expect to support
> here.  This file supports IOMMU API based usage of an IOMMU with
> effectively no DMA window or mapping constraints, optimized for static
> mapping of an address space.  What's a good name for that?  Maybe I
> should follow the example of others and just call it a Type 1 IOMMU
> implementation so the marketing material looks better!  ;-P  That may
> honestly be better than calling it x86.  Thoughts?  Thanks,
>
> Alex
I'll vote for 'type1' over 'x86' ....
Add a comment in the file what a 'type1 IOMMU' is.
Then others can dupe format for typeX.

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