intel-iommu: Dont cache iova above 32bit

Mike Travis and Mike Habeck reported an issue where iova allocation
would return a range that was larger than a device's dma mask.

https://lkml.org/lkml/2011/3/29/423



The dmar initialization code will reserve all PCI MMIO regions and copy
those reservations into a domain specific iova tree.  It is possible for
one of those regions to be above the dma mask of a device.  It is typical
to allocate iovas with a 32bit mask (despite device's dma mask possibly
being larger) and cache the result until it exhausts the lower 32bit
address space.  Freeing the iova range that is >= the last iova in the
lower 32bit range when there is still an iova above the 32bit range will
corrupt the cached iova by pointing it to a region that is above 32bit.
If that region is also larger than the device's dma mask, a subsequent
allocation will return an unusable iova and cause dma failure.

Simply don't cache an iova that is above the 32bit caching boundary.

Reported-by: Mike Travis <travis@sgi.com>
Reported-by: Mike Habeck <habeck@sgi.com>
Cc: stable@kernel.org
Acked-by: Mike Travis <travis@sgi.com>
Tested-by: Mike Habeck <habeck@sgi.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>