Re:Build your own Linux
by userbinator on Wednesday August 16, 2017 @11:10PM
(#15033513)
That applies only when you are actually using such an address for an access; you are free to store anything in those upper 16 bits as long as they are masked off when it's actually used to access memory.
"The AMD specification requires that the most significant 16 bits of any virtual address, bits 48 through 63, must be copies of bit 47 (in a manner akin to sign extension). If this requirement is not met, the processor will raise an exception."
https://en.wikipedia.org/wiki/X86-64#Virtual_address_space_d...