Orignally sent by Jisheng Zhang <jszhang@kernel.org>

This series tries to optimize riscv uaccess in the following way:

patch1 implement the user_access_begin and families, I.E the unsafe
accessors. when a function like strncpy_from_user() is called,
the userspace access protection is disabled and enabled for every
word read. After patch1, the protection is disabled at the beginning
of the copy and enabled at the end.

patch2 is a simple clean up

patch3 uses 'asm goto' for put_user()
patch4 uses 'asm goto output' for get_user()

Both patch3 and patch4 are based on the fact -- 'asm goto' and
'asm goto output'generates noticeably better code since we don't need
to test the error etc, the exception just jumps to the error handling
directly.

V2:
I've taken on this series as there isn't any response from Jisheng. No
significant changes other than build fixes.
- Fixes build breakage in patch 3 to do with not having used 'goto' keyword.
- Fixes build breakage in patch 4 on 32bit not having delcared __ptr in the
  macro.
I did read the discussion this series generated. It isn't clear to me
which direction to take the patches, if any.