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Wed, 16 Dec 2020 07:08:15 +0000 Subject: Re: [PATCH bpf-next v5 11/11] bpf: Document new atomic instructions To: Brendan Jackman , CC: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , KP Singh , Florent Revest , References: <20201215121816.1048557-1-jackmanb@google.com> <20201215121816.1048557-13-jackmanb@google.com> From: Yonghong Song Message-ID: Date: Tue, 15 Dec 2020 23:08:12 -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: <20201215121816.1048557-13-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::5:9412] X-ClientProxiedBy: MW4PR03CA0376.namprd03.prod.outlook.com (2603:10b6:303:114::21) 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:c085:21cf::12e6] (2620:10d:c090:400::5:9412) by MW4PR03CA0376.namprd03.prod.outlook.com (2603:10b6:303:114::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3654.12 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB4088.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Dec 2020 07:08:15.1391 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-Network-Message-Id: fc60af1b-79a5-4449-4513-08d8a1915ba1 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: ecn/8pGlEunPjOZt3gkEJoO5QztImD0mvq8x33hw2t4lJHBuPnTyC6pMUdvRsvwq X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3413 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-16_02:2020-12-15,2020-12-16 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 spamscore=0 suspectscore=0 bulkscore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=999 mlxscore=0 clxscore=1015 priorityscore=1501 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012160043 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 12/15/20 4:18 AM, Brendan Jackman wrote: > Document new atomic instructions. > > Signed-off-by: Brendan Jackman Ack with minor comments below. 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: Remove "(from architecture v4 onwards)". > + > + 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. Adding something like below. Except xadd for legacy reason, all other 4 byte atomic operations require alu32 mode. The alu32 mode can be enabled with clang flags "-Xclang -target-feature -Xclang +alu32" or "-mcpu=v3". The cpu version 3 has alu32 mode on by default. > > You may encounter BPF_XADD - this is a legacy name for BPF_ATOMIC, referring to >