On Thu, Apr 01, 2010 at 12:18:27PM -0700, Tom Lyon wrote: > On Thursday 01 April 2010 09:07:47 am Joerg Roedel wrote: > > 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. > > 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. The IOMMU-API allows that. You have to convert the user-virtual addresses into physical addresses first. The current KVM code already does this and uses the IOMMU-API later. You can have a look at the gfn_to_pfn() function for a way to implement this. > My preferred approach would be to add a DMA_ATTR that would request > allocation of DMA at a specific device/iommu address. No, that would be feature duplication between both APIs. Not to mention the implementation hell this additional dma-api feature would cause for the iommu driver developers. Joerg -- 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
