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

[Tom Lyon]

On Thursday 01 April 2010 02:09:09 am Avi Kivity wrote:
> On 04/01/2010 03:08 AM, Tom Lyon wrote:
> > uio_pci_generic has previously been discussed on the KVM list, but this
> > patch has nothing to do with KVM, so it is also going to LKML.
>
> (needs to go to lkml even if it was for kvm)
>
> > 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.
> >
> > Specifically, I seek to allow low-latency user level network drivers (non
> > tcp/ip) which directly access SR-IOV style virtual network adapters, for
> > use with packages such as OpenMPI.
> >
> > Key areas of change:
> > - ioctl extensions to allow registration and dma mapping of memory
> > regions, with lock accounting
> > - support for mmu notifier driven de-mapping
>
> Note that current iommus/devices don't support restart-on-fault dma, so
> userspace drivers will have to lock memory so that it is not swapped
> out.  I don't think this prevents page migration, though.
The driver provides a way to lock memory for DMA; the mmu notifier support is 
to catch things when the user accidentally frees locked pages.

> > - support for MSI and MSI-X interrupts (the intel 82599 VFs support only
> > MSI-X)
>
> How does a userspace program receive those interrupts?
Same as other UIO drivers - by read()ing an event counter.
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