x86/mm/32: Add support for 64-bit __get_user() on 32-bit kernels

x86/mm/32: Add support for 64-bit __get_user() on 32-bit kernels

The existing __get_user() implementation does not support fetching
64-bit values on 32-bit x86.  Implement this in a way that does not
generate any incorrect warnings as cautioned by Russell King.

Test code available at:

  http://www.kvack.org/~bcrl/x86_32-get_user.tar .

Signed-off-by: Benjamin LaHaise <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Ingo Molnar <[email protected]>