From: Daniel Borkmann daniel@iogearbox.net
commit 8968c67a82ab7501bc3b9439c3624a49b42fe54c upstream.
Prefetch-with-intent-to-write is currently part of the XADD mapping in the AArch64 JIT and follows the kernel's implementation of atomic_add. This may interfere with other threads executing the LDXR/STXR loop, leading to potential starvation and fairness issues. Drop the optional prefetch instruction.
Fixes: 85f68fe89832 ("bpf, arm64: implement jiting of BPF_XADD") Reported-by: Will Deacon will.deacon@arm.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Jean-Philippe Brucker jean-philippe.brucker@arm.com Acked-by: Will Deacon will.deacon@arm.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/net/bpf_jit.h | 6 ------ arch/arm64/net/bpf_jit_comp.c | 1 - 2 files changed, 7 deletions(-)
--- a/arch/arm64/net/bpf_jit.h +++ b/arch/arm64/net/bpf_jit.h @@ -100,12 +100,6 @@ #define A64_STXR(sf, Rt, Rn, Rs) \ A64_LSX(sf, Rt, Rn, Rs, STORE_EX)
-/* Prefetch */ -#define A64_PRFM(Rn, type, target, policy) \ - aarch64_insn_gen_prefetch(Rn, AARCH64_INSN_PRFM_TYPE_##type, \ - AARCH64_INSN_PRFM_TARGET_##target, \ - AARCH64_INSN_PRFM_POLICY_##policy) - /* Add/subtract (immediate) */ #define A64_ADDSUB_IMM(sf, Rd, Rn, imm12, type) \ aarch64_insn_gen_add_sub_imm(Rd, Rn, imm12, \ --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -739,7 +739,6 @@ emit_cond_jmp: case BPF_STX | BPF_XADD | BPF_DW: emit_a64_mov_i(1, tmp, off, ctx); emit(A64_ADD(1, tmp, tmp, dst), ctx); - emit(A64_PRFM(tmp, PST, L1, STRM), ctx); emit(A64_LDXR(isdw, tmp2, tmp), ctx); emit(A64_ADD(isdw, tmp2, tmp2, src), ctx); emit(A64_STXR(isdw, tmp2, tmp, tmp3), ctx);