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From: Brendan Jackman <jackmanb@google.com>
To: 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: [PATCH v2 bpf-next 13/13] bpf: Document new atomic instructions
Date: Fri, 27 Nov 2020 17:57:38 +0000	[thread overview]
Message-ID: <20201127175738.1085417-14-jackmanb@google.com> (raw)
In-Reply-To: <20201127175738.1085417-1-jackmanb@google.com>

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 Documentation/networking/filter.rst | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst
index 1583d59d806d..c86091b8cb0e 100644
--- a/Documentation/networking/filter.rst
+++ b/Documentation/networking/filter.rst
@@ -1053,6 +1053,33 @@ 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_SUB
+    BPF_AND
+    BPF_OR
+    BPF_XOR
+
+Each having isomorphic 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
+pre-modification value from memory.
+
+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 pre-modification
+value 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
-- 
2.29.2.454.gaff20da3a2-goog


  parent reply	other threads:[~2020-11-27 17:58 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-27 17:57 [PATCH v2 bpf-next 00/13] Atomics for eBPF Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 01/13] bpf: x86: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2020-11-29  1:15   ` Alexei Starovoitov
2020-12-01 12:14     ` Brendan Jackman
2020-12-02  5:50       ` Alexei Starovoitov
2020-12-02 10:52         ` Brendan Jackman
2020-12-02 17:35           ` Alexei Starovoitov
2020-11-27 17:57 ` [PATCH v2 bpf-next 02/13] bpf: x86: Factor out emission of REX byte Brendan Jackman
2020-11-29  1:14   ` Alexei Starovoitov
2020-12-01 12:12     ` Brendan Jackman
2020-12-02  5:48       ` Alexei Starovoitov
2020-12-02 10:54         ` Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 03/13] bpf: x86: Factor out function to emit NEG Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 04/13] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 05/13] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-11-28  3:43   ` Yonghong Song
2020-12-01 12:17     ` Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 06/13] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 07/13] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-11-28  4:15   ` Yonghong Song
2020-12-01 12:22     ` Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 08/13] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2020-11-28  5:25   ` Yonghong Song
2020-12-01 12:27     ` Brendan Jackman
2020-11-29  1:27   ` Alexei Starovoitov
2020-12-01 12:32     ` Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 09/13] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub Brendan Jackman
2020-11-27 21:39   ` kernel test robot
2020-11-27 21:39     ` kernel test robot
2020-11-27 21:39   ` [RFC PATCH] bpf: bpf_atomic_alu_string[] can be static kernel test robot
2020-11-27 21:39     ` kernel test robot
2020-11-28  5:35   ` [PATCH v2 bpf-next 10/13] bpf: Add instructions for atomic[64]_[fetch_]sub Yonghong Song
2020-11-29  1:34     ` Alexei Starovoitov
2020-11-30 17:18       ` Yonghong Song
2020-12-01 12:38         ` Brendan Jackman
2020-12-02  5:55           ` Alexei Starovoitov
2020-12-02 11:19             ` Brendan Jackman
2020-11-27 17:57 ` [PATCH v2 bpf-next 11/13] bpf: Add bitwise atomic instructions Brendan Jackman
2020-11-28  5:39   ` Yonghong Song
2020-11-29  1:36     ` Alexei Starovoitov
2020-11-30 17:20       ` Yonghong Song
2020-11-27 17:57 ` [PATCH v2 bpf-next 12/13] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-12-01  3:55   ` Yonghong Song
2020-12-01 12:56     ` Brendan Jackman
2020-12-01 17:24       ` Yonghong Song
2020-12-02  2:22   ` Andrii Nakryiko
2020-12-02 12:26     ` Brendan Jackman
2020-11-27 17:57 ` Brendan Jackman [this message]
2020-11-28  5:53 ` [PATCH v2 bpf-next 00/13] Atomics for eBPF Yonghong Song
2020-11-29  1:40   ` Alexei Starovoitov
2020-11-30 17:22     ` Yonghong Song
2020-12-01  3:48       ` Yonghong Song
2020-12-02  2:00         ` Andrii Nakryiko
2020-12-02  5:05           ` Yonghong Song
2020-12-02  5:53             ` John Fastabend
2020-12-02  5:59               ` Andrii Nakryiko
2020-12-02  6:27                 ` John Fastabend
2020-12-02  8:03             ` Yonghong Song

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