powerpc/64s/hash: add stress_hpt kernel boot option to increase hash faults

This option increases the number of hash misses by limiting the number
of kernel HPT entries, by keeping a per-CPU record of the last kernel
HPTEs installed, and removing that from the hash table on the next hash
insertion. A timer round-robins CPUs removing remaining kernel HPTEs and
clearing the TLB (in the case of bare metal) to increase and slightly
randomise kernel fault activity.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Add comment about NR_CPUS usage, fixup whitespace]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221024030150.852517-1-npiggin@gmail.com

powerpc/mm/64s: Fix no previous prototype warning

As reported by lkp:

arch/powerpc/mm/book3s64/radix_tlb.c:646:6: warning: no previous
prototype for function 'exit_lazy_flush_tlb'

Fix it by moving the prototype into the existing header.

Fixes: 032b7f08932c ("powerpc/64s/radix: serialize_against_pte_lookup IPIs trim mm_cpumask")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210210130804.3190952-2-mpe@ellerman.id.au

powerpc/mm/64s: Fix slb_setup_new_exec() sparse warning

Sparse says:
symbol slb_setup_new_exec was not declared. Should it be static?

No, it should have a declaration in a header, add one.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200916115637.3100484-1-mpe@ellerman.id.au

powerpc/64s/hash: Add stress_slb kernel boot option to increase SLB faults

This option increases the number of SLB misses by limiting the number
of kernel SLB entries, and increased flushing of cached lookaside
information. This helps stress test difficult to hit paths in the
kernel.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Relocate the code into arch/powerpc/mm, s/torture/stress/]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200511125825.3081305-1-mpe@ellerman.id.au