linux-kernel - Re: [PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm

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Message-ID: <bdc90ccd-e017-b7b1-7ba8-f5e261ad7296@fb.com>
Date:   Fri, 27 Nov 2020 19:43:46 -0800
From:   Yonghong Song <yhs@...com>
To:     Brendan Jackman <jackmanb@...gle.com>, <bpf@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        <linux-kernel@...r.kernel.org>, Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to
 encode other atomics in .imm



On 11/27/20 9:57 AM, 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@...gle.com>
> ---
>   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                   | 46 ++++++++++++++-----
>   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                        |  8 ++--
>   include/uapi/linux/bpf.h                      |  3 +-
>   kernel/bpf/core.c                             | 31 +++++++++----
>   kernel/bpf/disasm.c                           |  6 ++-
>   kernel/bpf/verifier.c                         | 24 ++++++----
>   lib/test_bpf.c                                |  2 +-
>   samples/bpf/bpf_insn.h                        |  4 +-
>   samples/bpf/sock_example.c                    |  2 +-
>   samples/bpf/test_cgrp2_attach.c               |  4 +-
>   tools/include/linux/filter.h                  |  7 +--
>   tools/include/uapi/linux/bpf.h                |  3 +-
>   .../bpf/prog_tests/cgroup_attach_multi.c      |  4 +-
>   tools/testing/selftests/bpf/verifier/ctx.c    |  7 ++-
>   .../testing/selftests/bpf/verifier/leak_ptr.c |  4 +-
>   tools/testing/selftests/bpf/verifier/unpriv.c |  3 +-
>   tools/testing/selftests/bpf/verifier/xadd.c   |  2 +-
>   30 files changed, 248 insertions(+), 120 deletions(-)
> 
> diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
[...]
> diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> index 0a721f6e8676..1c9efc74edfc 100644
> --- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> +++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
> @@ -3109,13 +3109,19 @@ mem_xadd(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta, bool is64)
>   	return 0;
>   }
>   
> -static int mem_xadd4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> +static int mem_atomic4(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
>   {
> +	if (meta->insn.off != BPF_ADD)
> +		return -EOPNOTSUPP;

You probably missed this change. it should be meta->insn.imm != BPF_ADD.

> +
>   	return mem_xadd(nfp_prog, meta, false);
>   }
>   
> -static int mem_xadd8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
> +static int mem_atomic8(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
>   {
> +	if (meta->insn.off != BPF_ADD)

same as above.

> +		return -EOPNOTSUPP;
> +
>   	return mem_xadd(nfp_prog, meta, true);
>   }
>   
> @@ -3475,8 +3481,8 @@ static const instr_cb_t instr_cb[256] = {
>   	[BPF_STX | BPF_MEM | BPF_H] =	mem_stx2,
>   	[BPF_STX | BPF_MEM | BPF_W] =	mem_stx4,
>   	[BPF_STX | BPF_MEM | BPF_DW] =	mem_stx8,
> -	[BPF_STX | BPF_XADD | BPF_W] =	mem_xadd4,
> -	[BPF_STX | BPF_XADD | BPF_DW] =	mem_xadd8,
> +	[BPF_STX | BPF_ATOMIC | BPF_W] =	mem_atomic4,
> +	[BPF_STX | BPF_ATOMIC | BPF_DW] =	mem_atomic8,
>   	[BPF_ST | BPF_MEM | BPF_B] =	mem_st1,
>   	[BPF_ST | BPF_MEM | BPF_H] =	mem_st2,
>   	[BPF_ST | BPF_MEM | BPF_W] =	mem_st4,
[...]