6.8-stable review patch. If anyone has any objections, please let me know.
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From: Ilya Leoshkevich iii@linux.ibm.com
[ Upstream commit 68378982f0b21de02ac3c6a11e2420badefcb4bc ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/s390/net/bpf_jit_comp.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 5af0402e94b88..1d168a98ae21b 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -1427,8 +1427,12 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, EMIT6_DISP_LH(0xeb000000, is32 ? (op32) : (op64), \ (insn->imm & BPF_FETCH) ? src_reg : REG_W0, \ src_reg, dst_reg, off); \ - if (is32 && (insn->imm & BPF_FETCH)) \ - EMIT_ZERO(src_reg); \ + if (insn->imm & BPF_FETCH) { \ + /* bcr 14,0 - see atomic_fetch_{add,and,or,xor}() */ \ + _EMIT2(0x07e0); \ + if (is32) \ + EMIT_ZERO(src_reg); \ + } \ } while (0) case BPF_ADD: case BPF_ADD | BPF_FETCH: