We don't use 1GB pages in the direct map today, and likely won't for some time. They aren't supported on all amd64 CPUs so if we decided we were interested in doing that, we'd need two types of direct map layouts, one to support CPUs that had 1GB page support and one that didn't. That seems like an awful lot of complexity for questionable gain.
edit: ... and if we did decide, in the future, to take advantage of 1GB page support in the direct map, I'd probably just break out the kernel area separately and continue to map it with 2MB pages.
edit: ... and if we did decide, in the future, to take advantage of 1GB page support in the direct map, I'd probably just break out the kernel area separately and continue to map it with 2MB pages.