Ilya Leoshkevich 68378982f0 s390/bpf: Emit a barrier for BPF_FETCH instructions ...

BPF_ATOMIC_OP() macro documentation states that "BPF_ADD | BPF_FETCH"
should be the same as atomic_fetch_add(), which is currently not the
case on s390x: the serialization instruction "bcr 14,0" is missing.
This applies to "and", "or" and "xor" variants too.

s390x is allowed to reorder stores with subsequent fetches from
different addresses, so code relying on BPF_FETCH acting as a barrier,
for example:

  stw [%r0], 1
  afadd [%r1], %r2
  ldxw %r3, [%r4]

may be broken. Fix it by emitting "bcr 14,0".

Note that a separate serialization instruction is not needed for
BPF_XCHG and BPF_CMPXCHG, because COMPARE AND SWAP performs
serialization itself.

Fixes: ba3b86b9cef0 ("s390/bpf: Implement new atomic ops")
Reported-by: Puranjay Mohan <puranjay12@gmail.com>
Closes: https://lore.kernel.org/bpf/mb61p34qvq3wf.fsf@kernel.org/
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20240507000557.12048-1-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2024-05-12 16:55:57 -07:00

..

bpf_jit_comp.c

s390/bpf: Emit a barrier for BPF_FETCH instructions

2024-05-12 16:55:57 -07:00

bpf_jit.h

bpf, s390x: remove ld_abs/ld_ind

2018-05-03 16:49:20 -07:00

Makefile

Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next

2018-06-06 18:39:49 -07:00

pnet.c

s390/net: convert pnetids to ascii

2019-02-21 10:34:37 -08:00