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bh=o+McSM2gKtujfwRfyeOsaE02Y4bKTLqqTyQF/lTUOqg=; b=Y5vLPveY2QUDx6KfKBhflOtt+Oz8RyeacYFYLdpIzW+8+btIshN5+lX5ezGw8mN9mH+lgH1Oxbx3ZTxOj4QWXMZNiovZOFhVtg7rEycCm8fAvL63Wqwnd8AJpWEWmfd5GIdZsetxwZd4pxRCm2PxraAel1HraUBtd3UCHXknjj4= Received: from CO1PR10MB4531.namprd10.prod.outlook.com (2603:10b6:303:6c::22) by LV3PR10MB7820.namprd10.prod.outlook.com (2603:10b6:408:1b4::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6521.23; Wed, 28 Jun 2023 18:52:54 +0000 Received: from CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::8b8f:b4b1:bb78:b048]) by CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::8b8f:b4b1:bb78:b048%5]) with mapi id 15.20.6521.024; Wed, 28 Jun 2023 18:52:53 +0000 From: Eric DeVolder To: linux-kernel@vger.kernel.org, david@redhat.com, osalvador@suse.de, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, bhe@redhat.com, ebiederm@xmission.com, kexec@lists.infradead.org Cc: hpa@zytor.com, gregkh@linuxfoundation.org, rafael@kernel.org, vgoyal@redhat.com, dyoung@redhat.com, lf32.dev@gmail.com, akpm@linux-foundation.org, naveen.n.rao@linux.vnet.ibm.com, zohar@linux.ibm.com, bhelgaas@google.com, vbabka@suse.cz, tiwai@suse.de, seanjc@google.com, linux@weissschuh.net, vschneid@redhat.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, sourabhjain@linux.ibm.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, eric.devolder@oracle.com Subject: [PATCH v24 10/10] x86/crash: optimize CPU changes Date: Wed, 28 Jun 2023 14:52:15 -0400 Message-Id: <20230628185215.40707-11-eric.devolder@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20230628185215.40707-1-eric.devolder@oracle.com> References: <20230628185215.40707-1-eric.devolder@oracle.com> X-ClientProxiedBy: SJ2PR07CA0019.namprd07.prod.outlook.com (2603:10b6:a03:505::21) To CO1PR10MB4531.namprd10.prod.outlook.com (2603:10b6:303:6c::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PR10MB4531:EE_|LV3PR10MB7820:EE_ X-MS-Office365-Filtering-Correlation-Id: e85c2bcc-b5f7-4902-dde9-08db7808e13a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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As such, subsequent changes to CPUs (ie. hot un/plug, online/offline) do not need to rewrite the elfcorehdr. The kimage->file_mode term covers kdump images loaded via the kexec_file_load() syscall. Since crash_prepare_elf64_headers() wrote the initial elfcorehdr, no update to the elfcorehdr is needed for CPU changes. The kimage->elfcorehdr_updated term covers kdump images loaded via the kexec_load() syscall. At least one memory or CPU change must occur to cause crash_prepare_elf64_headers() to rewrite the elfcorehdr. Afterwards, no update to the elfcorehdr is needed for CPU changes. This code is intentionally *NOT* hoisted into crash_handle_hotplug_event() as it would prevent the arch-specific handler from running for CPU changes. This would break PPC, for example, which needs to update other information besides the elfcorehdr, on CPU changes. Signed-off-by: Eric DeVolder Reviewed-by: Sourabh Jain Acked-by: Hari Bathini Acked-by: Baoquan He --- arch/x86/kernel/crash.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c index caf22bcb61af..18d2a18d1073 100644 --- a/arch/x86/kernel/crash.c +++ b/arch/x86/kernel/crash.c @@ -467,6 +467,16 @@ void arch_crash_handle_hotplug_event(struct kimage *image) unsigned long mem, memsz; unsigned long elfsz = 0; + /* + * As crash_prepare_elf64_headers() has already described all + * possible CPUs, there is no need to update the elfcorehdr + * for additional CPU changes. + */ + if ((image->file_mode || image->elfcorehdr_updated) && + ((image->hp_action == KEXEC_CRASH_HP_ADD_CPU) || + (image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU))) + return; + /* * Create the new elfcorehdr reflecting the changes to CPU and/or * memory resources.