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Tue, 8 Dec 2020 01:41:07 +0000 Subject: Re: [PATCH bpf-next v4 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction To: Brendan Jackman , CC: Alexei Starovoitov , Daniel Borkmann , KP Singh , Florent Revest , , Jann Horn References: <20201207160734.2345502-1-jackmanb@google.com> <20201207160734.2345502-7-jackmanb@google.com> From: Yonghong Song Message-ID: <4163e34b-754a-5607-c28a-4c575a2cc6e5@fb.com> Date: Mon, 7 Dec 2020 17:41:05 -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: <20201207160734.2345502-7-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:ee04] X-ClientProxiedBy: MW4PR04CA0335.namprd04.prod.outlook.com (2603:10b6:303:8a::10) 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:ee04) by MW4PR04CA0335.namprd04.prod.outlook.com (2603:10b6:303:8a::10) 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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> */ > > #define BPF_ATOMIC64(OP, DST, SRC, OFF) \ > @@ -201,6 +202,16 @@ > .off = OFF, \ > .imm = BPF_ADD }) > > +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(dst_reg + off, src_reg); */ > + > +#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \ > + ((struct bpf_insn) { \ > + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \ > + .dst_reg = DST, \ > + .src_reg = SRC, \ > + .off = OFF, \ > + .imm = BPF_ADD | BPF_FETCH }) Not sure whether it is a good idea or not to fold this into BPF_ATOMIC macro. At least you can define BPF_ATOMIC macro and #define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \ BPF_ATOMIC(SIZE, DST, SRC, OFF, BPF_ADD | BPF_FETCH) to avoid too many code duplications? > + > /* Memory store, *(uint *) (dst_reg + off16) = imm32 */ > > #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \ > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h > index 98161e2d389f..d5389119291e 100644 > --- a/tools/include/uapi/linux/bpf.h > +++ b/tools/include/uapi/linux/bpf.h > @@ -44,6 +44,9 @@ > #define BPF_CALL 0x80 /* function call */ > #define BPF_EXIT 0x90 /* function return */ > > +/* atomic op type fields (stored in immediate) */ > +#define BPF_FETCH 0x01 /* fetch previous value into src reg */ > + > /* Register numbers */ > enum { > BPF_REG_0 = 0, >