On 04/30/2013 05:15 PM, Alex Williamson wrote:
On Tue, 2013-04-30 at 16:48 -0400, Don Dutile wrote:
On 04/30/2013 03:11 PM, Konrad Rzeszutek Wilk wrote:
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.
no group support. probably doesn't have an iommu-like api either...
It doesn't, in fact uio-pci doesn't even allow enabling bus master
because there's zero isolation.
sounds like a no-iommu iommu interface is needed! :-p
(Alex: that slipped out! sorry!)
I wouldn't say "needed", I'm really not sure how or why this is even
practical. What would we do with a userspace driver interface that's
backed by a software IOMMU that provides neither translation nor
isolation? This is exactly why I suggested to the freescale guys that
it should be some kind of vfio-fake-iommu backend with very, very strict
capability checking and no default loading. Thanks,
Alex
that's what I would expect as well. but it's still a wonky fake-iommu...
writing code to do almost nothing.... sounds like pci-stub! :)
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