[PATCH v14 0/6] powerpc/crash: Kernel handling of CPU and memory hotplug

Sourabh Jain sourabhjain at linux.ibm.com
Mon Dec 11 19:30:50 AEDT 2023

Commit 247262756121 ("crash: add generic infrastructure for crash
hotplug support") added a generic infrastructure that allows
architectures to selectively update the kdump image component during CPU
or memory add/remove events within the kernel itself.

This patch series adds crash hotplug handler for PowerPC and enable
support to update the kdump image on CPU/Memory add/remove events.

Among the 6 patches in this series, the first three patches make changes
to the generic crash hotplug handler to assist PowerPC in adding support
for this feature. The last three patches add support for this feature.

The following section outlines the problem addressed by this patch
series, along with the current solution, its shortcomings, and the
proposed resolution.

Due to CPU/Memory hotplug or online/offline events the elfcorehdr
(which describes the CPUs and memory of the crashed kernel) and FDT
(Flattened Device Tree) of kdump image becomes outdated. Consequently,
attempting dump collection with an outdated elfcorehdr or FDT can lead
to failed or inaccurate dump collection.

Going forward CPU hotplug or online/offline events are referred as
CPU/Memory add/remove events.

Existing solution and its shortcoming:
The current solution to address the above issue involves monitoring the
CPU/memory add/remove events in userspace using udev rules and whenever
there are changes in CPU and memory resources, the entire kdump image
is loaded again. The kdump image includes kernel, initrd, elfcorehdr,
FDT, purgatory. Given that only elfcorehdr and FDT get outdated due to
CPU/Memory add/remove events, reloading the entire kdump image is
inefficient. More importantly, kdump remains inactive for a substantial
amount of time until the kdump reload completes.

Proposed solution:
Instead of initiating a full kdump image reload from userspace on
CPU/Memory hotplug and online/offline events, the proposed solution aims
to update only the necessary kdump image component within the kernel

Git tree for testing:
Git tree rebased on top of v6.7-rc4:

To realize this feature, the kdump udev rule must be updated. On RHEL,
add the following two lines at the top of the
"/usr/lib/udev/rules.d/98-kexec.rules" file.

SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"

With the above change to the kdump udev rule, kdump reload is avoided
during CPU/Memory add/remove events if this feature is enabled in the

Note: only kexec_file_load syscall will work. For kexec_load minor changes
are required in kexec tool.


  - Fix build warnings by including necessary header files
  - Rebase to v6.7-rc5

  - Fix a build warning, take ranges.c out of CONFIG_KEXEC_FILE
  - Rebase to v6.7-rc4

  - A patch to add new kexec flags to support this feature on kexec_load
    system call
  - Change in the way this feature is advertise to userspace for both
    kexec_load syscall
  - Rebase to v6.6-rc7

  - Rebase to v6.4-rc6
  - The patch that introduced CONFIG_CRASH_HOTPLUG for PowerPC has been
    removed. The config is now part of common configuration:

  - Drop the patch that adds fdt_index attribute to struct kimage_arch
    Find the fdt segment index when needed.
  - Added more details into commits messages.
  - Rebased onto 6.3.0-rc5

  - Removed patch to prepare elfcorehdr crash notes for possible CPUs.
    The patch is moved to generic patch series that introduces generic
    infrastructure for in kernel crash update.
  - Removed patch to pass the hotplug action type to the arch crash
    hotplug handler function. The generic patch series has introduced
    the hotplug action type in kimage struct.
  - Add detail commit message for better understanding.

  - Restrict fdt_index initialization to machine_kexec_post_load
    it work for both kexec_load and kexec_file_load.[3/8] Laurent Dufour

  - Updated the logic to find the number of offline core. [6/8]

  - Changed the logic to find the elfcore program header to accommodate
    future memory ranges due memory hotplug events. [8/8]

  - added a new config to configure this feature
  - pass hotplug action type to arch specific handler

  - Added crash memory hotplug support

  - Move fdt segment identification for kexec_load case to load path
    instead of crash hotplug handler
  - Keep new attribute defined under kimage_arch to track FDT segment
    under CONFIG_HOTPLUG_CPU config.

  - Update the logic to find the additional space needed for hotadd CPUs
    post kexec load. Refer "[RFC v4 PATCH 4/5] powerpc/crash hp: add crash
    hotplug support for kexec_file_load" patch to know more about the
  - Fix a couple of typo.
  - Replace pr_err to pr_info_once to warn user about memory hotplug
  - In crash hotplug handle exit the for loop if FDT segment is found.

  - Move fdt_index and fdt_index_vaild variables to kimage_arch struct.
  - Rebase patche on top of
  - Fixed warning reported by checpatch script

  - Use generic hotplug handler introduced by
    a significant change from v1.

Cc: Akhil Raj <lf32.dev at gmail.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Aneesh Kumar K.V <aneesh.kumar at kernel.org>
Cc: Baoquan He <bhe at redhat.com>
Cc: Borislav Petkov (AMD) <bp at alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Cc: Christophe Leroy <christophe.leroy at csgroup.eu>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Dave Young <dyoung at redhat.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Eric DeVolder <eric.devolder at oracle.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Hari Bathini <hbathini at linux.ibm.com>
Cc: Laurent Dufour <laurent.dufour at fr.ibm.com>
Cc: Mahesh Salgaonkar <mahesh at linux.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Mimi Zohar <zohar at linux.ibm.com>
Cc: Naveen N Rao <naveen at kernel.org>
Cc: Oscar Salvador <osalvador at suse.de>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Valentin Schneider <vschneid at redhat.com>
Cc: Vivek Goyal <vgoyal at redhat.com>
Cc: kexec at lists.infradead.org
Cc: x86 at kernel.org

Sourabh Jain (6):
  crash: forward memory_notify arg to arch crash hotplug handler
  crash: make CPU and Memory hotplug support reporting flexible
  crash: add a new kexec flag for FDT update
  powerpc/kexec: turn some static helper functions public
  powerpc: add crash CPU hotplug support
  powerpc: add crash memory hotplug support

 arch/powerpc/Kconfig                    |   4 +
 arch/powerpc/include/asm/kexec.h        |  25 ++
 arch/powerpc/include/asm/kexec_ranges.h |   1 +
 arch/powerpc/kexec/Makefile             |   4 +-
 arch/powerpc/kexec/core_64.c            | 369 ++++++++++++++++++++++++
 arch/powerpc/kexec/elf_64.c             |  12 +-
 arch/powerpc/kexec/file_load_64.c       | 211 +++-----------
 arch/powerpc/kexec/ranges.c             |  85 ++++++
 arch/x86/include/asm/kexec.h            |  10 +-
 arch/x86/kernel/crash.c                 |  23 +-
 include/linux/kexec.h                   |  21 +-
 include/uapi/linux/kexec.h              |   1 +
 kernel/crash_core.c                     |  37 ++-
 kernel/kexec.c                          |   2 +
 14 files changed, 605 insertions(+), 200 deletions(-)


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