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From: Tom Lyon on 1 Apr 2010 15:30
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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From: Tom Lyon on 1 Apr 2010 17:40
On Thursday 01 April 2010 08:54:14 am Avi Kivity wrote:
> On 04/01/2010 06:39 PM, Tom Lyon wrote:
> >>> - 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.
>
> IIRC the usual event counter is /dev/uioX, what's your event counter now?
>
> kvm really wants the event counter to be an eventfd, that allows hooking
> it directly to kvm (which can inject an interrupt on an eventfd_signal),
> can you adapt your patch to do this?

I looked further into eventfds - they seem the perfect solution for the
MSI/MSI-X interrupts. Will include in V2.
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From: Tom Lyon on 9 Apr 2010 12:50
Mea culpa.

On Friday 09 April 2010 02:08:55 am Joerg Roedel wrote:
> Btw. This patch posting is broken. It suffers from line-wraps which make
> it impossible to apply as-is. I was able to fix it but please consider
> this in your next posting.
>
> On Wed, Mar 31, 2010 at 05:12:35PM -0700, Tom Lyon wrote:
>
> > --- linux-2.6.33/drivers/uio/uio_pci_generic.c 2010-02-24
> > 10:52:17.000000000 -0800
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Unexpected line-wrap.
>
> I also got some whitespace warnings when trying to apply it. Please make
> sure you fix this in the next version too.
>
> Thanks,
>
> Joerg
>
>


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