On Wed, 11 Nov 2020 22:01:51 +1000, Nicholas Piggin wrote:

read_user_stack_slow that walks user address translation by hand is
only required on hash, because a hash fault can not be serviced from
"NMI" context (to avoid re-entering the hash code) so the user stack
can be mapped into Linux page tables but not accessible by the CPU.

Radix MMU mode does not have this restriction. A page fault failure
would indicate the page is not accessible via get_user_pages either,
so avoid this on radix.

Applied to powerpc/next.

[1/1] powerpc/64s/perf: perf interrupt does not have to get_user_pages to access user memory
      https://git.kernel.org/powerpc/c/987c426320cce72d1b28f55c8603b239e4f7187c

cheers