Re: RFC: vfio / iommu driver for hardware with no iommu

[Konrad Rzeszutek Wilk <konrad.wilk-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

> >>Does vfio work with swiotlb and if not, can/should swiotlb be
> >>extended? Or does the time and space overhead make it a moot point?
> >
> >It does not work with SWIOTLB as it uses the DMA API, not the IOMMU API.
> >
> I think you got it reversed.  vfio uses iommu api, not dma api.

Right.  That is what I was saying :-) SWIOTLB uses the DMA API, not
the IOMMU API. Hence it won't work with VFIO. Unless SWIOTLB implements
the IOMMU API.


> if vfio used dma api, swiotlb is configured as the default dma-ops interface
> and it could work (with more interfaces... domain-alloc, etc.).

<nods>
> 
> >It could be extended to use it. I was toying with this b/c for Xen to
> >use VFIO I would have to implement an Xen IOMMU driver that would basically
> >piggyback on the SWIOTLB (as Xen itself does the IOMMU parts and takes
> >care of all the hard work of securing each guest).
> >
> >But your requirement would be the same, so it might as well be an generic
> >driver called SWIOTLB-IOMMU driver.
> >
> >If you are up for writting I am up for reviewing/Ack-ing/etc.
> >
> >The complexity would be to figure out the VFIO group thing and how to assign
> >PCI B:D:F devices to the SWIOTLB-IOMMU driver. Perhaps the same way as
> >xen-pciback does (or pcistub). That is by writting the BDF in the "bind"
> >attribute in SysFS (or via a kernel parameter).
> >
> 
> Did uio provide this un-secure support, and just needs some attention upstream?

I don't recall how UIO did it. Not sure if it even had the group
support.