config changes

[Kyle McMartin]

On Tue, Jan 13, 2009 at 10:21:52PM +0100, Gerd Hoffmann wrote:
> Dave Jones wrote:
> > On Tue, Jan 13, 2009 at 09:55:27PM +0100, Gerd Hoffmann wrote:
> >  > Bill Nottingham wrote:
> >  > > Here's some proposed config changes.
> >  > 
> >  > Jumping on the wagon ;)
> >  > 
> >  > Can we enable CONFIG_DMAR please?  This turns on the IOMMU on intel
> >  > boxes, using VT-d.  Called "DMA Remapping" in intel speak, this is where
> >  > the config option name comes from.  Advantages:
> >  > 
> >  >   (1) 32bit PCI devices can DMA to memory above 4G, thus the need for
> >  >       swiotlb (i.e. bounce buffers) is gone.
> >  >   (2) It allows kvm to pass through PCI devices to guests securely.
> >  
> > The last time we tried this, it blew up a lot due to broken BIOSes.
> 
> Do you have bug numbers at hand?
> Searching for CONFIG_DMAR gives me "Zarro Boogs found".
> 
> > Maybe it's been improved enough to tolerate them, so we can probably
> > give it a spin in rawhide for a while to see what happens.
> 
> Well, it works for me.  Single test box only though.  As the machine in
> question actually has memory above 4G it is a nice speedup for kernel
> builds (sys time going down from ~15min to ~5min).
> 

I've just enabled it (and GFX_WA and FLOPPY_WA on x86_64.)

(I'm suprised it's x86_64 only, surely virtualization enabled i386 could
 benefit from DMA protection?)