Re: [PATCH qemu-kvm] device assignment: default requires IOMMU

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Thu, Dec 24, 2009 at 02:56:00PM +0800, Sheng Yang wrote:

> > > >And, of course, disabling the IOMMU requirement using the old:
> > > >
> > > >  -pcidevice host=[addr],dma=none
> > > >
> > > >or the newer:
> > > >
> > > >  -device pci-assign,host=[addr],iommu=0
> > > >
> > > >will do what it always did (not require an IOMMU, and fail to work
> > > >properly).
> > >
> > > Yay!
> > 
> > Sounds good to me. Though I am curious to know the reasoning
> > behind the current logic.
> > 
> Sounds pretty good. :)
> 
> I think maybe it due to we are interested in implementing PV DMA?

Yes, we are. The current defaults came from the desire to support both
pvdma and also 1-1 host mappings. There were patches floating around
for both. Having said that, I fully agree with this change---the
default should be to require IOMMU. Anything else is "highly
experimental".

Cheers,
Muli