[PATCH v2 0/5] Atomics support for eBPF on powerpc

[Hari Bathini]

This patchset adds atomic operations to the eBPF instruction set on
powerpc. The instructions that are added here can be summarised with
this list of kernel operations for ppc64:

* atomic[64]_[fetch_]add
* atomic[64]_[fetch_]and
* atomic[64]_[fetch_]or
* atomic[64]_[fetch_]xor
* atomic[64]_xchg
* atomic[64]_cmpxchg

and this list of kernel operations for ppc32:

* atomic_[fetch_]add
* atomic_[fetch_]and
* atomic_[fetch_]or
* atomic_[fetch_]xor
* atomic_xchg
* atomic_cmpxchg

The following are left out of scope for this effort:

* 64 bit operations on ppc32.
* Explicit memory barriers, 16 and 8 bit operations on both ppc32
  & ppc64.

The first patch adds support for bitwsie atomic operations on ppc64.
The next patch adds fetch variant support for these instructions. The
third patch adds support for xchg and cmpxchg atomic operations on
ppc64. Patch #4 adds support for 32-bit atomic bitwise operations on
ppc32. patch #5 adds support for xchg and cmpxchg atomic operations
on ppc32.

Validated these changes successfully with atomics test cases in
test_bpf testsuite and  test_verifier & test_progs selftests.
With test_bpf testsuite:

  all 147 atomics related test cases (both 32-bit & 64-bit) JIT'ed
  successfully on ppc64:

    test_bpf: Summary: 1026 PASSED, 0 FAILED, [1014/1014 JIT'ed]

  all 76 atomics related test cases (32-bit) JIT'ed successfully
  on ppc32:

    test_bpf: Summary: 1027 PASSED, 0 FAILED, [915/1015 JIT'ed]

Changes in v2:
* Moved variable declaration to avoid late declaration error on
  some compilers. Thanks to Russell for pointing this out.
* For ppc64, added an optimization for 32-bit cmpxchg with regard
  to commit 39491867ace5.
* For ppc32, used an additional register (BPF_REG_AX):
    - to avoid clobbering src_reg.
    - to keep the lwarx reservation as intended.
    - to avoid the odd switch/goto construct.
* For ppc32, zero'ed out the higher 32-bit explicitly when required.


Hari Bathini (5):
  bpf ppc64: add support for BPF_ATOMIC bitwise operations
  bpf ppc64: add support for atomic fetch operations
  bpf ppc64: Add instructions for atomic_[cmp]xchg
  bpf ppc32: add support for BPF_ATOMIC bitwise operations
  bpf ppc32: Add instructions for atomic_[cmp]xchg

 arch/powerpc/net/bpf_jit_comp32.c | 72 +++++++++++++++++++----
 arch/powerpc/net/bpf_jit_comp64.c | 96 ++++++++++++++++++++++---------
 2 files changed, 129 insertions(+), 39 deletions(-)

-- 
2.35.3