Messages in this thread Patch in this message | | | From | Eric DeVolder <> | Subject | [PATCH v25 10/10] x86/crash: optimize CPU changes | Date | Thu, 29 Jun 2023 15:21:19 -0400 |
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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 <eric.devolder@oracle.com> Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com> Acked-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Baoquan He <bhe@redhat.com> --- 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. -- 2.31.1
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