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Sat, 11 Jul 2020 06:28:45 +0000 From: Song Liu To: Andrii Nakryiko CC: open list , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , john fastabend , KP Singh , Jesper Dangaard Brouer , Peter Ziljstra Subject: Re: [PATCH bpf-next 1/5] bpf: block bpf_get_[stack|stackid] on perf_event with PEBS entries Thread-Topic: [PATCH bpf-next 1/5] bpf: block bpf_get_[stack|stackid] on perf_event with PEBS entries Thread-Index: AQHWVyKzhisy7cu33UCexze8SbKGKKkBv0iAgAArfwA= Date: Sat, 11 Jul 2020 06:28:45 +0000 Message-ID: References: <20200711012639.3429622-1-songliubraving@fb.com> <20200711012639.3429622-2-songliubraving@fb.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.80.23.2.2) authentication-results: gmail.com; dkim=none (message not signed) header.d=none;gmail.com; dmarc=none action=none header.from=fb.com; x-originating-ip: [2620:10d:c090:400::5:f0b7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 046d5471-edf8-404b-9f76-08d82563aa1d x-ms-traffictypediagnostic: BYAPR15MB2454: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:5516; 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charset="us-ascii" Content-ID: <01818A7A6E0BCE4D969F17D94EE6E372@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB2999.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 046d5471-edf8-404b-9f76-08d82563aa1d X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Jul 2020 06:28:45.7514 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: GbowPEgYCTRfIQVfCVtaj+RiIvU/tCEjir5Tt0Yiqoz59wsWW4yWsuRHr7+5sLne3fta6FNZoosUnMzgIlZlWg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2454 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-07-10_14:2020-07-10,2020-07-10 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 priorityscore=1501 mlxscore=0 adultscore=0 mlxlogscore=999 phishscore=0 malwarescore=0 lowpriorityscore=0 bulkscore=0 impostorscore=0 spamscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007110047 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org > On Jul 10, 2020, at 8:53 PM, Andrii Nakryiko = wrote: >=20 > On Fri, Jul 10, 2020 at 6:30 PM Song Liu wrote: >>=20 >> Calling get_perf_callchain() on perf_events from PEBS entries may cause >> unwinder errors. To fix this issue, the callchain is fetched early. Such >> perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY. >>=20 >> Similarly, calling bpf_get_[stack|stackid] on perf_events from PEBS may >> also cause unwinder errors. To fix this, block bpf_get_[stack|stackid] o= n >> these perf_events. Unfortunately, bpf verifier cannot tell whether the >> program will be attached to perf_event with PEBS entries. Therefore, >> block such programs during ioctl(PERF_EVENT_IOC_SET_BPF). >>=20 >> Signed-off-by: Song Liu >> --- >=20 > Perhaps it's a stupid question, but why bpf_get_stack/bpf_get_stackid > can't figure out automatically that they are called from > __PERF_SAMPLE_CALLCHAIN_EARLY perf event and use different callchain, > if necessary? >=20 > It is quite suboptimal from a user experience point of view to require > two different BPF helpers depending on PEBS or non-PEBS perf events. I am not aware of an easy way to tell the difference in bpf_get_stack.=20 But I do agree that would be much better.=20 Thanks, Song=