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charset="us-ascii" Content-ID: <13EAA6F97D869B4D82650F2B36EB02E9@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 06acedb0-e5cd-4ce3-fe96-08d72be14fe7 X-MS-Exchange-CrossTenant-originalarrivaltime: 28 Aug 2019 17:58:20.3275 (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: VSw1bVRWbB3zWZunmUEtGlvOFgToY9l7HA6daHucAJW4brXI01zAF18xUb23G82Fh24zGCEwOW/XXrFPm3UoGQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1360 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.70,1.0.8 definitions=2019-08-28_08:2019-08-28,2019-08-28 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1015 spamscore=0 lowpriorityscore=0 adultscore=0 priorityscore=1501 bulkscore=0 malwarescore=0 phishscore=0 impostorscore=0 mlxlogscore=965 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1906280000 definitions=main-1908280175 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Aug 28, 2019, at 8:51 AM, Thomas Gleixner wrote: >=20 > On Wed, 28 Aug 2019, Dave Hansen wrote: >> On 8/28/19 7:24 AM, Thomas Gleixner wrote: >>> From: Song Liu >>>=20 >>> pti_clone_pmds() assumes that the supplied address is either: >>>=20 >>> - properly PUD/PMD aligned >>> or >>> - the address is actually mapped which means that independent >>> of the mapping level (PUD/PMD/PTE) the next higher mapping >>> exist. >>>=20 >>> If that's not the case the unaligned address can be incremented by PUD = or >>> PMD size wrongly. All callers supply mapped and/or aligned addresses, b= ut >>> for robustness sake, it's better to handle that case proper and to emit= a >>> warning. >>=20 >> Reviewed-by: Dave Hansen >>=20 >> Song, did you ever root-cause the performance regression? I thought >> there were still some mysteries there. >=20 > See Peter's series to rework the ftrace code patching ... Thanks Thomas.=20 Yes, in summary, enabling ftrace or kprobe-on-ftrace causes the kernel to split PMDs in kernel text mapping.=20 Related question: while Peter's patches fix it for 5.3 kernel, they don't=20 apply cleanly over 5.2 kernel (which we are using). So I wonder what is the best solution for 5.2 kernel. May patch also fixes the issue: https://lore.kernel.org/lkml/20190823052335.572133-1-songliubraving@fb.com/ How about we apply this patch to upstream 5.2 kernel? Thanks, Song