64 bit operations w/32 bit kernel

["Finney, Steve" <Steve.Finney@SpirentCom.COM>]

What would be the downside to enabling 64 bit operations in user space on a 32 
bit kernel (setting the PX bit in the status register?). The particular issue 
is that I want to access 64 bit-memory mapped registers, and I really need to 
do it as an atomic operation. I tried borrowing sibyte/64bit.h from the kernel, 
but I get an illegal instruction on the double ops.

Also, assuming this isn't a horrible idea, is there any obvious single place 
where "default" values in the CP0 status register get set?

Thanks,
sf