queue-4.19/bpf-arm64-remove-prefetch-insn-in-xadd-mapping.patch

   1 From 8968c67a82ab7501bc3b9439c3624a49b42fe54c Mon Sep 17 00:00:00 2001
   2 From: Daniel Borkmann <daniel@iogearbox.net>
   3 Date: Fri, 26 Apr 2019 21:48:21 +0200
   4 Subject: bpf, arm64: remove prefetch insn in xadd mapping
   5
   6 From: Daniel Borkmann <daniel@iogearbox.net>
   7
   8 commit 8968c67a82ab7501bc3b9439c3624a49b42fe54c upstream.
   9
  10 Prefetch-with-intent-to-write is currently part of the XADD mapping in
  11 the AArch64 JIT and follows the kernel's implementation of atomic_add.
  12 This may interfere with other threads executing the LDXR/STXR loop,
  13 leading to potential starvation and fairness issues. Drop the optional
  14 prefetch instruction.
  15
  16 Fixes: 85f68fe89832 ("bpf, arm64: implement jiting of BPF_XADD")
  17 Reported-by: Will Deacon <will.deacon@arm.com>
  18 Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
  19 Acked-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
  20 Acked-by: Will Deacon <will.deacon@arm.com>
  21 Signed-off-by: Alexei Starovoitov <ast@kernel.org>
  22 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  23
  24 ---
  25  arch/arm64/net/bpf_jit.h      |    6 ------
  26  arch/arm64/net/bpf_jit_comp.c |    1 -
  27  2 files changed, 7 deletions(-)
  28
  29 --- a/arch/arm64/net/bpf_jit.h
  30 +++ b/arch/arm64/net/bpf_jit.h
  31 @@ -100,12 +100,6 @@
  32  #define A64_STXR(sf, Rt, Rn, Rs) \
  33         A64_LSX(sf, Rt, Rn, Rs, STORE_EX)
  34
  35 -/* Prefetch */
  36 -#define A64_PRFM(Rn, type, target, policy) \
  37 -       aarch64_insn_gen_prefetch(Rn, AARCH64_INSN_PRFM_TYPE_##type, \
  38 -                                 AARCH64_INSN_PRFM_TARGET_##target, \
  39 -                                 AARCH64_INSN_PRFM_POLICY_##policy)
  40 -
  41  /* Add/subtract (immediate) */
  42  #define A64_ADDSUB_IMM(sf, Rd, Rn, imm12, type) \
  43         aarch64_insn_gen_add_sub_imm(Rd, Rn, imm12, \
  44 --- a/arch/arm64/net/bpf_jit_comp.c
  45 +++ b/arch/arm64/net/bpf_jit_comp.c
  46 @@ -736,7 +736,6 @@ emit_cond_jmp:
  47         case BPF_STX | BPF_XADD | BPF_DW:
  48                 emit_a64_mov_i(1, tmp, off, ctx);
  49                 emit(A64_ADD(1, tmp, tmp, dst), ctx);
  50 -               emit(A64_PRFM(tmp, PST, L1, STRM), ctx);
  51                 emit(A64_LDXR(isdw, tmp2, tmp), ctx);
  52                 emit(A64_ADD(isdw, tmp2, tmp2, src), ctx);
  53                 emit(A64_STXR(isdw, tmp2, tmp, tmp3), ctx);