linux-kernel - Re: [PATCH 0/1] uio_pci_generic: extensions to allow access for non-privileged processes

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Date:	Thu, 1 Apr 2010 18:07:47 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Tom Lyon <pugs@...n-about.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] uio_pci_generic: extensions to allow access for
	non-privileged processes

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

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