The patch titled
Subject: x86/crash: optimize CPU changes
has been added to the -mm mm-nonmm-unstable branch. Its filename is
x86-crash-optimize-cpu-changes.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-crash-optimize-cpu-changes.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Eric DeVolder <eric.devolder@xxxxxxxxxx>
Subject: x86/crash: optimize CPU changes
Date: Fri, 11 Aug 2023 13:06:42 -0400
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.
Link: https://lkml.kernel.org/r/20230811170642.6696-9-eric.devolder@xxxxxxxxxx
Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
Reviewed-by: Sourabh Jain <sourabhjain@xxxxxxxxxxxxx>
Acked-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
Acked-by: Baoquan He <bhe@xxxxxxxxxx>
Cc: Akhil Raj <lf32.dev@xxxxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Takashi Iwai <tiwai@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Thomas WeiÃ?schuh <linux@xxxxxxxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/crash.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/arch/x86/kernel/crash.c~x86-crash-optimize-cpu-changes
+++ a/arch/x86/kernel/crash.c
@@ -468,6 +468,16 @@ void arch_crash_handle_hotplug_event(str
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.
*/
_
Patches currently in -mm which might be from eric.devolder@xxxxxxxxxx are
kexec-consolidate-kexec-and-crash-options-into-kernel-kconfigkexec.patch
x86-kexec-refactor-for-kernel-kconfigkexec.patch
arm-kexec-refactor-for-kernel-kconfigkexec.patch
ia64-kexec-refactor-for-kernel-kconfigkexec.patch
arm64-kexec-refactor-for-kernel-kconfigkexec.patch
loongarch-kexec-refactor-for-kernel-kconfigkexec.patch
m68k-kexec-refactor-for-kernel-kconfigkexec.patch
mips-kexec-refactor-for-kernel-kconfigkexec.patch
parisc-kexec-refactor-for-kernel-kconfigkexec.patch
powerpc-kexec-refactor-for-kernel-kconfigkexec.patch
riscv-kexec-refactor-for-kernel-kconfigkexec.patch
s390-kexec-refactor-for-kernel-kconfigkexec.patch
sh-kexec-refactor-for-kernel-kconfigkexec.patch
kexec-rename-arch_has_kexec_purgatory.patch
remove-arch_default_kexec-from-kconfigkexec.patch
crash-move-a-few-code-bits-to-setup-support-of-crash-hotplug.patch
crash-add-generic-infrastructure-for-crash-hotplug-support.patch
kexec-exclude-elfcorehdr-from-the-segment-digest.patch
crash-memory-and-cpu-hotplug-sysfs-attributes.patch
x86-crash-add-x86-crash-hotplug-support.patch
crash-hotplug-support-for-kexec_load.patch
crash-change-crash_prepare_elf64_headers-to-for_each_possible_cpu.patch
x86-crash-optimize-cpu-changes.patch
