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2022 21:02:22 +0000 Message-ID: <7a7407d3-3ff0-4fea-2ea2-39ffda606138@meta.com> Date: Tue, 18 Oct 2022 17:02:20 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.3.3 Subject: Re: [PATCH bpf-next 3/3] libbpf: add non-mmapable data section selftest Content-Language: en-US From: Dave Marchevsky To: Andrii Nakryiko , bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net Cc: kernel-team@fb.com References: <20221018035646.1294873-1-andrii@kernel.org> <20221018035646.1294873-4-andrii@kernel.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MN2PR04CA0006.namprd04.prod.outlook.com (2603:10b6:208:d4::19) To DM6PR15MB4039.namprd15.prod.outlook.com (2603:10b6:5:2b2::20) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR15MB4039:EE_|BLAPR15MB3906:EE_ X-MS-Office365-Filtering-Correlation-Id: 0274631f-9e6d-4387-5718-08dab14c0d2c X-FB-Source: Internal 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ztlquSuLx+Au5b3OkT9eNFPpdRoYrQVnudRLoHJMPE9YbjqbzLwsPItV6CPRau3gHb9gkF7+q1ApRvq5Ny6S/g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLAPR15MB3906 X-Proofpoint-GUID: RyCnENhDg2KDqPMRVveT9opkapitLW01 X-Proofpoint-ORIG-GUID: RyCnENhDg2KDqPMRVveT9opkapitLW01 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-10-18_07,2022-10-18_01,2022-06-22_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 10/18/22 4:56 PM, Dave Marchevsky wrote: > On 10/17/22 11:56 PM, Andrii Nakryiko wrote: >> Add non-mmapable data section to test_skeleton selftest and make sure it >> really isn't mmapable by trying to mmap() it anyways. >> >> Also make sure that libbpf doesn't report BPF_F_MMAPABLE flag to users. >> >> Additional, some more manual testing was performed that this feature >> works as intended. >> >> Looking at created map through bpftool shows that flags passed to kernel are >> indeed zero: >> >> $ bpftool map show >> ... >> 1782: array name .data.non_mmapa flags 0x0 >> key 4B value 16B max_entries 1 memlock 4096B >> btf_id 1169 >> pids test_progs(8311) >> ... >> >> Checking BTF uploaded to kernel for this map shows that zero_key and >> zero_value are indeed marked as static, even though zero_key is actually >> original global (but STV_HIDDEN) variable: >> >> $ bpftool btf dump id 1169 >> ... >> [51] VAR 'zero_key' type_id=2, linkage=static >> [52] VAR 'zero_value' type_id=7, linkage=static >> ... >> [62] DATASEC '.data.non_mmapable' size=16 vlen=2 >> type_id=51 offset=0 size=4 (VAR 'zero_key') >> type_id=52 offset=4 size=12 (VAR 'zero_value') >> ... >> >> And original BTF does have zero_key marked as linkage=global: >> >> $ bpftool btf dump file test_skeleton.bpf.linked3.o >> ... >> [51] VAR 'zero_key' type_id=2, linkage=global >> [52] VAR 'zero_value' type_id=7, linkage=static >> ... >> [62] DATASEC '.data.non_mmapable' size=16 vlen=2 >> type_id=51 offset=0 size=4 (VAR 'zero_key') >> type_id=52 offset=4 size=12 (VAR 'zero_value') >> >> Bpftool didn't require any changes at all because it checks whether internal >> map is mmapable already, but just to double-check generated skeleton, we >> see that .data.non_mmapable neither sets mmaped pointer nor has >> a corresponding field in the skeleton: >> >> $ grep non_mmapable test_skeleton.skel.h >> struct bpf_map *data_non_mmapable; >> s->maps[7].name = ".data.non_mmapable"; >> s->maps[7].map = &obj->maps.data_non_mmapable; >> >> But .data.read_mostly has all of those things: >> >> $ grep read_mostly test_skeleton.skel.h >> struct bpf_map *data_read_mostly; >> struct test_skeleton__data_read_mostly { >> int read_mostly_var; >> } *data_read_mostly; >> s->maps[6].name = ".data.read_mostly"; >> s->maps[6].map = &obj->maps.data_read_mostly; >> s->maps[6].mmaped = (void **)&obj->data_read_mostly; >> _Static_assert(sizeof(s->data_read_mostly->read_mostly_var) == 4, "unexpected size of 'read_mostly_var'"); >> >> Signed-off-by: Andrii Nakryiko >> --- > > Signed-off-by: Dave Marchevsky Bah, I meant Acked-by: Dave Marchevsky