From: John Fastabend <john.fastabend@gmail.com>
To: Brendan Jackman <jackmanb@google.com>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>, Yonghong Song <yhs@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
KP Singh <kpsingh@chromium.org>,
Florent Revest <revest@chromium.org>,
linux-kernel@vger.kernel.org, Jann Horn <jannh@google.com>,
Brendan Jackman <jackmanb@google.com>
Subject: RE: [PATCH bpf-next v4 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction
Date: Mon, 07 Dec 2020 21:31:40 -0800 [thread overview]
Message-ID: <5fcf0fbcc8aa8_9ab320853@john-XPS-13-9370.notmuch> (raw)
In-Reply-To: <20201207160734.2345502-7-jackmanb@google.com>
Brendan Jackman wrote:
> The BPF_FETCH field can be set in bpf_insn.imm, for BPF_ATOMIC
> instructions, in order to have the previous value of the
> atomically-modified memory location loaded into the src register
> after an atomic op is carried out.
>
> Suggested-by: Yonghong Song <yhs@fb.com>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> ---
I like Yonghong suggestion
#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \
BPF_ATOMIC(SIZE, DST, SRC, OFF, BPF_ADD | BPF_FETCH)
otherwise LGTM. One observation to consider below.
Acked-by: John Fastabend <john.fastabend@gmail.com>
> arch/x86/net/bpf_jit_comp.c | 4 ++++
> include/linux/filter.h | 1 +
> include/uapi/linux/bpf.h | 3 +++
> kernel/bpf/core.c | 13 +++++++++++++
> kernel/bpf/disasm.c | 7 +++++++
> kernel/bpf/verifier.c | 33 ++++++++++++++++++++++++---------
> tools/include/linux/filter.h | 11 +++++++++++
> tools/include/uapi/linux/bpf.h | 3 +++
> 8 files changed, 66 insertions(+), 9 deletions(-)
[...]
> @@ -3652,8 +3656,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> return err;
>
> /* check whether we can write into the same memory */
> - return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> - BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> + err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> + BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> + if (err)
> + return err;
> +
> + if (!(insn->imm & BPF_FETCH))
> + return 0;
> +
> + /* check and record load of old value into src reg */
> + err = check_reg_arg(env, insn->src_reg, DST_OP);
This will mark the reg unknown. I think this is fine here. Might be nice
to carry bounds through though if possible
> + if (err)
> + return err;
> +
> + return 0;
> }
>
next prev parent reply other threads:[~2020-12-08 5:32 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 16:07 [PATCH bpf-next v4 00/11] Atomics for eBPF Brendan Jackman
2020-12-07 16:07 ` [PATCH bpf-next v4 01/11] bpf: x86: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2020-12-07 21:04 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 02/11] bpf: x86: Factor out emission of REX byte Brendan Jackman
2020-12-07 21:07 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 03/11] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2020-12-07 21:08 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 04/11] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-12-07 21:56 ` John Fastabend
2020-12-08 9:26 ` Brendan Jackman
2020-12-09 5:40 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 05/11] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-12-08 1:35 ` Yonghong Song
2020-12-08 5:13 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-12-08 1:41 ` Yonghong Song
2020-12-08 9:31 ` Brendan Jackman
2020-12-08 5:31 ` John Fastabend [this message]
2020-12-08 9:59 ` Brendan Jackman
2020-12-07 16:07 ` [PATCH bpf-next v4 07/11] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2020-12-08 1:44 ` Yonghong Song
2020-12-08 6:37 ` John Fastabend
2020-12-14 15:39 ` Brendan Jackman
2020-12-08 6:42 ` John Fastabend
2020-12-07 16:07 ` [PATCH bpf-next v4 08/11] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2020-12-07 16:07 ` [PATCH bpf-next v4 09/11] bpf: Add bitwise atomic instructions Brendan Jackman
2020-12-08 1:47 ` Yonghong Song
2020-12-10 0:22 ` kernel test robot
2020-12-07 16:07 ` [PATCH bpf-next v4 10/11] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-12-08 3:18 ` Yonghong Song
2020-12-08 12:41 ` Brendan Jackman
2020-12-08 16:38 ` Yonghong Song
2020-12-08 16:59 ` Brendan Jackman
2020-12-08 18:15 ` Yonghong Song
2020-12-15 11:12 ` Brendan Jackman
2020-12-16 7:18 ` Yonghong Song
2020-12-16 11:51 ` Brendan Jackman
2020-12-16 20:00 ` Yonghong Song
2020-12-07 16:07 ` [PATCH bpf-next v4 11/11] bpf: Document new atomic instructions Brendan Jackman
2020-12-08 3:25 ` Yonghong Song
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