On Thursday 01 April 2010 09:07:47 am Joerg Roedel wrote: > On Thu, Apr 01, 2010 at 08:40:34AM -0700, Tom Lyon wrote: > > On Thursday 01 April 2010 05:52:18 am Joerg Roedel wrote: > > > > The point of this patch is to beef up the uio_pci_generic driver so > > > > that a non-privileged user process can run a user level driver for > > > > most PCIe devices. This can only be safe if there is an IOMMU in the > > > > system with per-device domains. Privileged users (CAP_SYS_RAWIO) are > > > > allowed if there is no IOMMU. > > > > > > If you rely on an IOMMU you can use the IOMMU-API instead of the > > > DMA-API for dma mappings. This change makes this driver suitable for > > > KVM use too. If the interface is designed clever enough we can even use > > > it for IOMMU emulation for pass-through devices. > > > > The use with privileged processes and no IOMMUs is still quite useful, so > > I'd rather stick with the DMA interface. > > For the KVM use-case we need to be able to specify the io virtual > address for a given process virtual address. This is not possible with > the dma-api interface. So if we want to have uio-dma without an hardware > iommu we need two distinct interfaces for userspace to cover all > use-cases. I don't think its worth it to have two interfaces. > > Joerg I started to add that capability but then realized that the IOMMU API also doesn't allow it. The map function allows a range of physically contiguous pages, not virtual. My preferred approach would be to add a DMA_ATTR that would request allocation of DMA at a specific device/iommu address. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
