Re: [PATCH 0/1] uio_pci_generic: extensions to allow access fornon-privileged processes

From: Joerg Roedel
Date: Thu Apr 01 2010 - 12:07:59 EST

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.


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