From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 0/1] uio_pci_generic: extensions to allow access for non-privileged processes Date: Thu, 1 Apr 2010 22:09:10 +0200 Message-ID: <20100401200910.GJ24846@8bytes.org> References: <201003311708.38961.pugs@lyon-about.com> <201004010840.34574.pugs@lyon-about.com> <20100401160746.GH24846@8bytes.org> <201004011218.28002.pugs@lyon-about.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Tom Lyon Return-path: Content-Disposition: inline In-Reply-To: <201004011218.28002.pugs@lyon-about.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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