Messages in this thread | | | From | Tom Lyon <> | Subject | Re: [PATCH 0/1] uio_pci_generic: extensions to allow access for non-privileged processes | Date | Thu, 1 Apr 2010 12:18:27 -0700 |
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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.
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