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Tue, 8 Dec 2020 03:25:19 +0000 Subject: Re: [PATCH bpf-next v4 11/11] bpf: Document new atomic instructions To: Brendan Jackman , CC: Alexei Starovoitov , Daniel Borkmann , KP Singh , Florent Revest , , Jann Horn References: <20201207160734.2345502-1-jackmanb@google.com> <20201207160734.2345502-12-jackmanb@google.com> From: Yonghong Song Message-ID: <7b82cf2c-e7d0-0969-d5ce-2d3341b31a52@fb.com> Date: Mon, 7 Dec 2020 19:25:16 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 In-Reply-To: <20201207160734.2345502-12-jackmanb@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [2620:10d:c090:400::5:4c73] X-ClientProxiedBy: MW4PR04CA0002.namprd04.prod.outlook.com (2603:10b6:303:69::7) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21c8::113f] (2620:10d:c090:400::5:4c73) by MW4PR04CA0002.namprd04.prod.outlook.com (2603:10b6:303:69::7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3632.21 via Frontend Transport; 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Acked-by: Yonghong Song > --- > 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: No "v4" any more. Just say The basic atomic operations supported 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. For 4-byte operations, except BPF_ADD, alu32 mode is required. alu32 is implied with -mcpu=v3. > + > +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 >