RE: [PATCH bpf-next v4 04/11] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm

From: John Fastabend
Date: Mon Dec 07 2020 - 16:57:52 EST

Brendan Jackman wrote:
> A subsequent patch will add additional atomic operations. These new
> operations will use the same opcode field as the existing XADD, with
> the immediate discriminating different operations.
>
> In preparation, rename the instruction mode BPF_ATOMIC and start
> calling the zero immediate BPF_ADD.
>
> This is possible (doesn't break existing valid BPF progs) because the
> immediate field is currently reserved MBZ and BPF_ADD is zero.
>
> All uses are removed from the tree but the BPF_XADD definition is
> kept around to avoid breaking builds for people including kernel
> headers.
>
> Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
> ---
> Documentation/networking/filter.rst | 30 ++++++++-----
> arch/arm/net/bpf_jit_32.c | 7 ++-
> arch/arm64/net/bpf_jit_comp.c | 16 +++++--
> arch/mips/net/ebpf_jit.c | 11 +++--
> arch/powerpc/net/bpf_jit_comp64.c | 25 ++++++++---
> arch/riscv/net/bpf_jit_comp32.c | 20 +++++++--
> arch/riscv/net/bpf_jit_comp64.c | 16 +++++--
> arch/s390/net/bpf_jit_comp.c | 27 ++++++-----
> arch/sparc/net/bpf_jit_comp_64.c | 17 +++++--
> arch/x86/net/bpf_jit_comp.c | 45 ++++++++++++++-----
> arch/x86/net/bpf_jit_comp32.c | 6 +--
> drivers/net/ethernet/netronome/nfp/bpf/jit.c | 14 ++++--
> drivers/net/ethernet/netronome/nfp/bpf/main.h | 4 +-
> .../net/ethernet/netronome/nfp/bpf/verifier.c | 15 ++++---
> include/linux/filter.h | 29 ++++++++++--
> include/uapi/linux/bpf.h | 5 ++-
> kernel/bpf/core.c | 31 +++++++++----
> kernel/bpf/disasm.c | 6 ++-
> kernel/bpf/verifier.c | 24 +++++-----
> lib/test_bpf.c | 14 +++---
> samples/bpf/bpf_insn.h | 4 +-
> samples/bpf/cookie_uid_helper_example.c | 6 +--
> samples/bpf/sock_example.c | 2 +-
> samples/bpf/test_cgrp2_attach.c | 5 ++-
> tools/include/linux/filter.h | 28 ++++++++++--
> tools/include/uapi/linux/bpf.h | 5 ++-
> .../bpf/prog_tests/cgroup_attach_multi.c | 4 +-
> .../selftests/bpf/test_cgroup_storage.c | 2 +-
> tools/testing/selftests/bpf/verifier/ctx.c | 7 ++-
> .../bpf/verifier/direct_packet_access.c | 4 +-
> .../testing/selftests/bpf/verifier/leak_ptr.c | 10 ++---
> .../selftests/bpf/verifier/meta_access.c | 4 +-
> tools/testing/selftests/bpf/verifier/unpriv.c | 3 +-
> .../bpf/verifier/value_illegal_alu.c | 2 +-
> tools/testing/selftests/bpf/verifier/xadd.c | 18 ++++----
> 35 files changed, 317 insertions(+), 149 deletions(-)
>

[...]

> +++ a/arch/mips/net/ebpf_jit.c

[...]

> - if (BPF_MODE(insn->code) == BPF_XADD) {
> + if (BPF_MODE(insn->code) == BPF_ATOMIC) {
> + if (insn->imm != BPF_ADD) {
> + pr_err("ATOMIC OP %02x NOT HANDLED\n", insn->imm);
> + return -EINVAL;
> + }
> +
> /*
[...]
> +++ b/arch/powerpc/net/bpf_jit_comp64.c

> - case BPF_STX | BPF_XADD | BPF_W:
> + case BPF_STX | BPF_ATOMIC | BPF_W:
> + if (insn->imm != BPF_ADD) {
> + pr_err_ratelimited(
> + "eBPF filter atomic op code %02x (@%d) unsupported\n",
> + code, i);
> + return -ENOTSUPP;
> + }
[...]
> @@ -699,8 +707,15 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
> - case BPF_STX | BPF_XADD | BPF_DW:
> + case BPF_STX | BPF_ATOMIC | BPF_DW:
> + if (insn->imm != BPF_ADD) {
> + pr_err_ratelimited(
> + "eBPF filter atomic op code %02x (@%d) unsupported\n",
> + code, i);
> + return -ENOTSUPP;
> + }
[...]
> + case BPF_STX | BPF_ATOMIC | BPF_W:
> + if (insn->imm != BPF_ADD) {
> + pr_info_once(
> + "bpf-jit: not supported: atomic operation %02x ***\n",
> + insn->imm);
> + return -EFAULT;
> + }
[...]
> + case BPF_STX | BPF_ATOMIC | BPF_W:
> + case BPF_STX | BPF_ATOMIC | BPF_DW:
> + if (insn->imm != BPF_ADD) {
> + pr_err("bpf-jit: not supported: atomic operation %02x ***\n",
> + insn->imm);
> + return -EINVAL;
> + }

Can we standardize the error across jits and the error return code? It seems
odd that we use pr_err, pr_info_once, pr_err_ratelimited and then return
ENOTSUPP, EFAULT or EINVAL.

granted the error codes might not propagate all the way out at the moment but
still shouldn't hurt.

> diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> index 0a4182792876..f973e2ead197 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -1205,18 +1205,23 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,

For example this will return -1 regardless of error from insn->imm != BPF_ADD.
[...]
> + case BPF_STX | BPF_ATOMIC | BPF_DW:
> + case BPF_STX | BPF_ATOMIC | BPF_W:
> + if (insn->imm != BPF_ADD) {
> + pr_err("Unknown atomic operation %02x\n", insn->imm);
> + return -1;
> + }
> +
[...]

> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -259,15 +259,38 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
> .off = OFF, \
> .imm = 0 })
>
> -/* Atomic memory add, *(uint *)(dst_reg + off16) += src_reg */
> +
> +/*
> + * Atomic operations:
> + *
> + * BPF_ADD *(uint *) (dst_reg + off16) += src_reg
> + */
> +
> +#define BPF_ATOMIC64(OP, DST, SRC, OFF) \
> + ((struct bpf_insn) { \
> + .code = BPF_STX | BPF_DW | BPF_ATOMIC, \
> + .dst_reg = DST, \
> + .src_reg = SRC, \
> + .off = OFF, \
> + .imm = OP })
> +
> +#define BPF_ATOMIC32(OP, DST, SRC, OFF) \
> + ((struct bpf_insn) { \
> + .code = BPF_STX | BPF_W | BPF_ATOMIC, \
> + .dst_reg = DST, \
> + .src_reg = SRC, \
> + .off = OFF, \
> + .imm = OP })
> +
> +/* Legacy equivalent of BPF_ATOMIC{64,32}(BPF_ADD, ...) */

Not sure I care too much. Does seem more natural to follow
below pattern and use,

BPF_ATOMIC(OP, SIZE, DST, SRC, OFF)

>
> #define BPF_STX_XADD(SIZE, DST, SRC, OFF) \
> ((struct bpf_insn) { \
> - .code = BPF_STX | BPF_SIZE(SIZE) | BPF_XADD, \
> + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \
> .dst_reg = DST, \
> .src_reg = SRC, \
> .off = OFF, \
> - .imm = 0 })
> + .imm = BPF_ADD })
>
> /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
>

[...]

Otherwise LGTM, I'll try to get the remaining patches reviewed tonight
I need to jump onto something else this afternoon. Thanks!