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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 v28 8/8] x86/crash: optimize CPU changes Date: Mon, 14 Aug 2023 17:44:46 -0400 Message-Id: <20230814214446.6659-9-eric.devolder@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20230814214446.6659-1-eric.devolder@oracle.com> References: <20230814214446.6659-1-eric.devolder@oracle.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SN4PR0501CA0007.namprd05.prod.outlook.com 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linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" crash_prepare_elf64_headers() writes into the elfcorehdr an ELF PT_NOTE for all possible CPUs. 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 1900efcdf1bc..86d2ca80b9b2 100644 --- a/arch/x86/kernel/crash.c +++ b/arch/x86/kernel/crash.c @@ -469,6 +469,16 @@ void arch_crash_handle_hotplug_event(struct kimage *im= age) unsigned long mem, memsz; unsigned long elfsz =3D 0; =20 + /* + * 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 =3D=3D KEXEC_CRASH_HP_ADD_CPU) || + (image->hp_action =3D=3D KEXEC_CRASH_HP_REMOVE_CPU))) + return; + /* * Create the new elfcorehdr reflecting the changes to CPU and/or * memory resources. --=20 2.31.1