I've been wanting to do this for years, to run a multi-seat box (multiple users on one machine, each with their own kbd+mouse+vga). I was disappointed a couple years ago when I got a core2 to find out that even with HW virt support, giving the guest direct VGA access wasn't possible.
What current and future x86-64 hardware has an IOMMU suitable for guest video drivers? Anyone more up to date on this than I am?
Like I said it's more complicated then normal hardware. DMA isn't the issue. Video cards are special cases and you have to have support in the vbios themselves for this sort of thing.