From: Brendan Jackman <jackmanb@google.com>
To: bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
KP Singh <kpsingh@chromium.org>,
Florent Revest <revest@chromium.org>,
linux-kernel@vger.kernel.org,
Brendan Jackman <jackmanb@google.com>
Subject: [PATCH bpf-next v5 11/11] bpf: Document new atomic instructions
Date: Tue, 15 Dec 2020 12:18:16 +0000 [thread overview]
Message-ID: <20201215121816.1048557-13-jackmanb@google.com> (raw)
In-Reply-To: <20201215121816.1048557-1-jackmanb@google.com>
Document new atomic instructions.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
Documentation/networking/filter.rst | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index 1583d59d806d..26d508a5e038 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1053,6 +1053,32 @@ encoding.
.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
+The basic atomic operations supported (from architecture v4 onwards) are:
+
+ BPF_ADD
+ BPF_AND
+ BPF_OR
+ BPF_XOR
+
+Each having equivalent semantics with the ``BPF_ADD`` example, that is: the
+memory location addresed by ``dst_reg + off`` is atomically modified, with
+``src_reg`` as the other operand. If the ``BPF_FETCH`` flag is set in the
+immediate, then these operations also overwrite ``src_reg`` with the
+value that was in memory before it was modified.
+
+The more special operations are:
+
+ BPF_XCHG
+
+This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg +
+off``.
+
+ BPF_CMPXCHG
+
+This atomically compares the value addressed by ``dst_reg + off`` with
+``R0``. If they match it is replaced with ``src_reg``, The value that was there
+before is loaded back to ``R0``.
+
Note that 1 and 2 byte atomic operations are not supported.
You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to
--
2.29.2.684.gfbc64c5ab5-goog
next prev parent reply other threads:[~2020-12-15 12:21 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 12:18 [PATCH bpf-next v4 00/11] Atomics for eBPF Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 01/11] bpf: x86: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v2] libbpf: Expose libbpf ringbufer epoll_fd Brendan Jackman
2020-12-15 18:35 ` Andrii Nakryiko
2020-12-15 12:18 ` [PATCH bpf-next v5 02/11] bpf: x86: Factor out emission of REX byte Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 03/11] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 04/11] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-12-15 14:05 ` Björn Töpel
2020-12-15 12:18 ` [PATCH bpf-next v5 05/11] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 07/11] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2020-12-16 6:47 ` Yonghong Song
2020-12-15 12:18 ` [PATCH bpf-next v5 08/11] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2020-12-15 12:18 ` [PATCH bpf-next v5 09/11] bpf: Add bitwise atomic instructions Brendan Jackman
2020-12-16 6:53 ` Yonghong Song
2020-12-15 12:18 ` [PATCH bpf-next v5 10/11] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-12-15 12:18 ` Brendan Jackman [this message]
2020-12-16 7:08 ` [PATCH bpf-next v5 11/11] bpf: Document new atomic instructions Yonghong Song
2020-12-16 11:44 ` Brendan Jackman
2020-12-16 15:25 ` Yonghong Song
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