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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 bpf-next v3 14/14] bpf: Document new atomic instructions
Date: Thu,  3 Dec 2020 16:02:45 +0000	[thread overview]
Message-ID: <20201203160245.1014867-15-jackmanb@google.com> (raw)
In-Reply-To: <20201203160245.1014867-1-jackmanb@google.com>

Change-Id: Ic70fe9e3cb4403df4eb3be2ea5ae5af53156559e
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
-- 
2.29.2.454.gaff20da3a2-goog


  parent reply	other threads:[~2020-12-03 16:05 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-03 16:02 [PATCH bpf-next v3 00/14] Atomics for eBPF Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 01/14] bpf: x86: Factor out emission of ModR/M for *(reg + off) Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 02/14] bpf: x86: Factor out emission of REX byte Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 03/14] bpf: x86: Factor out function to emit NEG Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 04/14] bpf: x86: Factor out a lookup table for some ALU opcodes Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 05/14] bpf: Rename BPF_XADD and prepare to encode other atomics in .imm Brendan Jackman
2020-12-04  4:49   ` Yonghong Song
2020-12-03 16:02 ` [PATCH bpf-next v3 06/14] bpf: Move BPF_STX reserved field check into BPF_STX verifier code Brendan Jackman
2020-12-04  4:51   ` Yonghong Song
2020-12-03 16:02 ` [PATCH bpf-next v3 07/14] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction Brendan Jackman
2020-12-04  5:02   ` Yonghong Song
2020-12-04  5:27   ` Yonghong Song
2020-12-04  9:12     ` Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 08/14] bpf: Add instructions for atomic_[cmp]xchg Brendan Jackman
2020-12-04  5:34   ` Yonghong Song
2020-12-04  9:26     ` Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 09/14] bpf: Pull out a macro for interpreting atomic ALU operations Brendan Jackman
2020-12-04  6:30   ` Yonghong Song
2020-12-04  9:29     ` Brendan Jackman
2020-12-04 15:20       ` Yonghong Song
2020-12-03 16:02 ` [PATCH bpf-next v3 10/14] bpf: Add bitwise atomic instructions Brendan Jackman
2020-12-04  6:42   ` Yonghong Song
2020-12-04  9:36     ` Brendan Jackman
2020-12-04 15:21       ` Yonghong Song
2020-12-07 11:28         ` Brendan Jackman
2020-12-07 15:58           ` Yonghong Song
2020-12-07 16:14             ` Brendan Jackman
2020-12-03 16:02 ` [PATCH bpf-next v3 11/14] tools build: Implement feature check for BPF atomics in Clang Brendan Jackman
2020-12-03 21:02   ` Andrii Nakryiko
2020-12-03 16:02 ` [PATCH bpf-next v3 12/14] bpf: Pull tools/build/feature biz into selftests Makefile Brendan Jackman
2020-12-03 21:01   ` Andrii Nakryiko
2020-12-04  9:41     ` Brendan Jackman
2020-12-04 19:00       ` Andrii Nakryiko
2020-12-07 11:00         ` Brendan Jackman
2020-12-08  2:19           ` Andrii Nakryiko
2020-12-08 17:04             ` Brendan Jackman
2020-12-08 18:31               ` Andrii Nakryiko
2020-12-03 16:02 ` [PATCH bpf-next v3 13/14] bpf: Add tests for new BPF atomic operations Brendan Jackman
2020-12-04  7:06   ` Yonghong Song
2020-12-04  9:45     ` Brendan Jackman
2020-12-04 15:28       ` Yonghong Song
2020-12-04 19:49         ` Andrii Nakryiko
2020-12-07 15:48           ` Brendan Jackman
2020-12-03 16:02 ` Brendan Jackman [this message]
2020-12-03 16:10 ` [PATCH bpf-next v3 00/14] Atomics for eBPF Brendan Jackman
2020-12-04  4:46 ` Yonghong Song

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