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 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
