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Cc: Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, mgorman@suse.de, peterz@infradead.org, rostedt@goodmis.org, tglx@linutronix.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH v2 3/9] mm/huge_page: cleanup clear_/copy_subpage() In-reply-to: Date: Mon, 11 Sep 2023 10:22:33 -0700 Message-ID: <877cow1v6u.fsf@oracle.com> Content-Type: text/plain X-ClientProxiedBy: MW4PR04CA0154.namprd04.prod.outlook.com (2603:10b6:303:85::9) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO6PR10MB5409:EE_|DM4PR10MB7526:EE_ X-MS-Office365-Filtering-Correlation-Id: 25680709-875c-4abd-be47-08dbb2ebb08f X-MS-Exchange-SenderADCheck: 1 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g6K2C7PPuTcOYlwRSnR52fty/5RPc7Ym4AlQobMhuU8uavyGaZ1mInVBhaxPJaIuQXRkDHhpU41igOYas6np9ZnOi1Wf6dIHVoSJvPOTj5A= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR10MB7526 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-09-11_13,2023-09-05_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 mlxscore=0 adultscore=0 phishscore=0 spamscore=0 suspectscore=0 malwarescore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2308100000 definitions=main-2309110158 X-Proofpoint-GUID: zGbaMngwIcUOAChws3OAvQMontOvnP7l X-Proofpoint-ORIG-GUID: zGbaMngwIcUOAChws3OAvQMontOvnP7l Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Matthew Wilcox writes: > On Wed, Aug 30, 2023 at 11:49:52AM -0700, Ankur Arora wrote: >> @@ -5945,9 +5935,7 @@ static int __clear_huge_page( >> /* Process subpages at the end of huge page */ >> for (i = pages_per_huge_page - 1; i >= 2 * n; i--) { >> cond_resched(); >> - ret = process_subpage(addr + i * PAGE_SIZE, i, arg); >> - if (ret) >> - return ret; >> + clear_user_highpage(page + i, addr + i * PAGE_SIZE); > > It's possible for a 1GB page to cross a memmap discontiguity. This > needs to be: > > clear_user_highpage(nth_page(page, i), > addr + i * PAGE_SIZE); > > (similarly in other places) Thanks, will fix. I see that the pre-patch version of clear_gigantic_page() does the right thing: for (i = 0; i < pages_per_huge_page; i++) { p = nth_page(page, i); cond_resched(); clear_user_highpage(p, addr + i * PAGE_SIZE); } But, the clear_subpage() does not: clear_user_highpage(page + idx, addr); I think that got missed in 14455eabd840 ("mm: use nth_page instead of mem_map_offset mem_map_next"). Should I be sending a patch to stable? Also, for my testing, what's the config option where you would see a memmap discontiguity? Thanks -- ankur