Messages in this thread | | | Date | Tue, 7 Mar 2023 14:30:09 +0530 | Subject | Re: [PATCH v19 7/7] x86/crash: optimize cpu changes | From | Sourabh Jain <> |
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On 06/03/23 21:52, Eric DeVolder wrote: > This patch is dependent upon the patch 'crash: change > crash_prepare_elf64_headers() to for_each_possible_cpu()'. With that > patch, crash_prepare_elf64_headers() writes out an ELF cpu PT_NOTE > for all possible cpus, thus further cpu changes to the elfcorehdr > are not needed. > > This change works for kexec_file_load() and kexec_load() syscalls. > For kexec_file_load(), crash_prepare_elf64_headers() is utilized > directly and thus all ELF cpu PT_NOTEs are in the elfcorehdr already. > This is the kimage->file_mode term. > For kexec_load() syscall, one cpu or memory change will cause the > elfcorehdr to be updated via crash_prepare_elf64_headers() and at > that point all ELF cpu PT_NOTEs are in the elfcorehdr. This is the > kimage->elfcorehdr_updated term. > > 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> > --- > 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 c9aaec9de775..82ea2b1bdc61 100644 > --- a/arch/x86/kernel/crash.c > +++ b/arch/x86/kernel/crash.c > @@ -471,6 +471,16 @@ 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. This works for both kexec_load() > + * and kexec_file_load() syscalls. > + */ > + if ((image->file_mode || image->elfcorehdr_updated) && > + ((image->hp_action == KEXEC_CRASH_HP_ADD_CPU) || > + (image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU))) > + return;
I like the idea of having elfcorehdr_updated to track elfcoredhr segment updates. It handles the possible CPU thing for kexec_load syscall nicely.
Thanks for incorporating the possible CPU change.
The patch series looks good to me. Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
- Sourabh Jain
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