On Thu, 7 Aug 2008, H. Peter Anvin wrote:Just moving it down by 4 MB doesn't help, since the VMI guys want as much as
64 MB, which is half the standard vmalloc area and hence too much address
space lost. We can't put it at the bottom of the vmalloc area, since that
boundary is not fixed, either.
Yeah, ok. Since this is a 32-bit only issue, 64MB is actually a fair chunk of our already limited virtual space.
The one remaining fixed boundary in the machine is the kernel-userspace
boundary. Hence moving the 1:1 area up by one PDE unit and sticking the
fixmap area in that region.
Yeah, ok, but I'd be more nervous about the validation issues there. There might be a lot of code that assumes that TASK_SIZE is the start of the 1:1 area. It does sound like a good approach, it just makes me worry about the test coverage.