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SubjectRe: [PATCH] VFIO driver: Non-privileged user level PCI drivers
On Mon, Jun 07, 2010 at 12:01:04PM -0700, Tom Lyon wrote:
> On Sunday 06 June 2010 02:54:51 am Michael S. Tsirkin wrote:
> > On Thu, Jun 03, 2010 at 02:41:38PM -0700, Tom Lyon wrote:
> > > OK, in the interest of making progress, I am about to embark on the following:
> > >
> > > 1. Create a user-iommu-domain driver - opening it will give a new empty domain.
> > > Ultimately this can also populate sysfs with the state of its world, which would
> > > also be a good addition to the base iommu stuff.
> > > If someone closes the fd while in use, the domain stays valid anyway until users
> > > drop off.
> > >
> > > 2. Add DOMAIN_SET and DOMAIN_UNSET ioctls to the vfio driver. Require that
> > > a domain be set before using the VFIO_DMA_MAP_IOVA ioctl
> >
> > Require domain to be set before you allow any access to the device:
> > mmap, write, read. IMO this is the only safe way to make sure userspace
> > does not corrupt memory, and this removes the need to special-case
> > MSI memory, play with bus master enable and hope it can be cleared without
> > reset, etc.
>
> Michael - the light bulb finally lit for me and I now understand what you've been
> saying the past few weeks. Of course you're right - we need iommu set before any
> register access. I had thought that was done by default but now I see that the
> dma_map_sg routine only attaches to the iommu on demand.
>
> So I will torpedo the MAP_ANYWHERE stuff. I'd like to keep the MAP_IOVA ioctl
> with the vfio fd so that the user can still do everything with one fd. I'm thinking the
> fd opens and iommu bindings could be done in a program before spinning out the
> program with the user driver.

This would kind of break Avi's idea that mappings are programmed
at the domain and shared by multiple devices, won't it?

> >
> > > (this is the one
> > > that KVM wants).
> >
> > Not sure I understand. I think that MAP should be done on the domain,
> > not the device, this handles pinning pages correctly and
> > this way you don't need any special checks.
> >
> > > However, the VFIO_DMA_MAP_ANYWHERE ioctl is the one
> > > which uses the dma_sg interface which has no expicit control of domains. I
> > > intend to keep it the way it is, but expect only non-hypervisor programs would
> > > want to use it.
> >
> > If we support MAP_IOVA, why is MAP_ANYWHERE useful? Can't
> > non-hypervisors just pick an address?
> >
> > > 3. Clean up the docs and other nits that folks have found.
> > >
> > > Comments?
> >
>


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