x86: Document get_user_pages_fast()
x86: Document get_user_pages_fast()

While better than get_user_pages(), the usage of gupf(),
especially the return values and the fact that it can
potentially only partially pin the range, warranted some
documentation.

Signed-off-by: Andy Grover <f97dd4ff5f39846680e670bd8c5a456390ee8b8b@oracle.com>
Cc: 24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@suse.de
Cc: 5c1e68b099950c134891f0b6e179498a8ebe9cf9@linux-foundation.org
LKML-Reference: <1239320729-3262-1-git-send-email-f97dd4ff5f39846680e670bd8c5a456390ee8b8b@oracle.com>
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>

TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas