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charset="us-ascii" Content-ID: <79D026E569F0AA46B482192DD9973000@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 60626cab-ea37-4425-bd2c-08d72578abc4 X-MS-Exchange-CrossTenant-originalarrivaltime: 20 Aug 2019 14:14:10.2985 (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: eqzwCjLO1Elr0SE4H+Q94NsHuKHtJSLD6IsfWEB596pLdYurJDkknyjZhmQmn+MA3lHbaR/is7hWm9twvrN3cw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1519 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-20_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=980 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908200144 X-FB-Internal: deliver X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Aug 20, 2019, at 6:57 AM, Dave Hansen wrote: >=20 > On 8/20/19 12:51 AM, Song Liu wrote: >> In our x86_64 kernel, pti_clone_pgtable() fails to clone 7 PMDs because >> of this issuse, including PMD for the irq entry table. For a memcache >> like workload, this introduces about 4.5x more iTLB-load and about 2.5x >> more iTLB-load-misses on a Skylake CPU. >=20 > I was surprised that this manifests as a performance issue. Usually > messing up PTI page table manipulation means you get to experience the > jobs of debugging triple faults. But, it makes sense if its this line: >=20 > /* > * Note that this will undo _some_ of the work that > * pti_set_kernel_image_nonglobal() did to clear the > * global bit. > */ > pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE); >=20 > which is restoring the Global bit. >=20 > *But*, that shouldn't get hit on a Skylake CPU since those have PCIDs > and shouldn't have a global kernel image. Could you confirm whether > PCIDs are supported on this CPU? Yes, pcid is listed in /proc/cpuinfo.=20 Thanks, Song