6.8-stable review patch. If anyone has any objections, please let me know.
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From: Puranjay Mohan puranjay@kernel.org
[ Upstream commit 20a759df3bba35bf5c3ddec0c02ad69b603b584c ]
The BPF atomic operations with the BPF_FETCH modifier along with BPF_XCHG and BPF_CMPXCHG are fully ordered but the RISC-V JIT implements all atomic operations except BPF_CMPXCHG with relaxed ordering.
Section 8.1 of the "The RISC-V Instruction Set Manual Volume I: Unprivileged ISA" [1], titled, "Specifying Ordering of Atomic Instructions" says:
| To provide more efficient support for release consistency [5], each | atomic instruction has two bits, aq and rl, used to specify additional | memory ordering constraints as viewed by other RISC-V harts.
and
| If only the aq bit is set, the atomic memory operation is treated as | an acquire access. | If only the rl bit is set, the atomic memory operation is treated as a | release access. | | If both the aq and rl bits are set, the atomic memory operation is | sequentially consistent.
Fix this by setting both aq and rl bits as 1 for operations with BPF_FETCH and BPF_XCHG.
[1] https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf
Fixes: dd642ccb45ec ("riscv, bpf: Implement more atomic operations for RV64") Signed-off-by: Puranjay Mohan puranjay@kernel.org Reviewed-by: Pu Lehui pulehui@huawei.com Link: https://lore.kernel.org/r/20240505201633.123115-1-puranjay@kernel.org Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/net/bpf_jit_comp64.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c index 0bd747d1d00fc..29f031f68f480 100644 --- a/arch/riscv/net/bpf_jit_comp64.c +++ b/arch/riscv/net/bpf_jit_comp64.c @@ -516,33 +516,33 @@ static void emit_atomic(u8 rd, u8 rs, s16 off, s32 imm, bool is64, break; /* src_reg = atomic_fetch_<op>(dst_reg + off16, src_reg) */ case BPF_ADD | BPF_FETCH: - emit(is64 ? rv_amoadd_d(rs, rs, rd, 0, 0) : - rv_amoadd_w(rs, rs, rd, 0, 0), ctx); + emit(is64 ? rv_amoadd_d(rs, rs, rd, 1, 1) : + rv_amoadd_w(rs, rs, rd, 1, 1), ctx); if (!is64) emit_zext_32(rs, ctx); break; case BPF_AND | BPF_FETCH: - emit(is64 ? rv_amoand_d(rs, rs, rd, 0, 0) : - rv_amoand_w(rs, rs, rd, 0, 0), ctx); + emit(is64 ? rv_amoand_d(rs, rs, rd, 1, 1) : + rv_amoand_w(rs, rs, rd, 1, 1), ctx); if (!is64) emit_zext_32(rs, ctx); break; case BPF_OR | BPF_FETCH: - emit(is64 ? rv_amoor_d(rs, rs, rd, 0, 0) : - rv_amoor_w(rs, rs, rd, 0, 0), ctx); + emit(is64 ? rv_amoor_d(rs, rs, rd, 1, 1) : + rv_amoor_w(rs, rs, rd, 1, 1), ctx); if (!is64) emit_zext_32(rs, ctx); break; case BPF_XOR | BPF_FETCH: - emit(is64 ? rv_amoxor_d(rs, rs, rd, 0, 0) : - rv_amoxor_w(rs, rs, rd, 0, 0), ctx); + emit(is64 ? rv_amoxor_d(rs, rs, rd, 1, 1) : + rv_amoxor_w(rs, rs, rd, 1, 1), ctx); if (!is64) emit_zext_32(rs, ctx); break; /* src_reg = atomic_xchg(dst_reg + off16, src_reg); */ case BPF_XCHG: - emit(is64 ? rv_amoswap_d(rs, rs, rd, 0, 0) : - rv_amoswap_w(rs, rs, rd, 0, 0), ctx); + emit(is64 ? rv_amoswap_d(rs, rs, rd, 1, 1) : + rv_amoswap_w(rs, rs, rd, 1, 1), ctx); if (!is64) emit_zext_32(rs, ctx); break;